diff --git a/browser/components/about/AboutRedirector.cpp b/browser/components/about/AboutRedirector.cpp
index 9927a11420e7..1471e10bf0db 100644
--- a/browser/components/about/AboutRedirector.cpp
+++ b/browser/components/about/AboutRedirector.cpp
@@ -156,7 +156,7 @@ AboutRedirector::NewChannel(nsIURI* aURI, nsILoadInfo* aLoadInfo,
   // startup cache.
   if (XRE_IsContentProcess() && path.EqualsLiteral("home")) {
     auto& remoteType = dom::ContentChild::GetSingleton()->GetRemoteType();
-    if (remoteType == PRIVILEGEDABOUT_REMOTE_TYPE) {
+    if (remoteType.EqualsLiteral(PRIVILEGEDABOUT_REMOTE_TYPE)) {
       nsCOMPtr<nsIAboutNewTabService> aboutNewTabService =
           do_GetService("@mozilla.org/browser/aboutnewtab-service;1", &rv);
       NS_ENSURE_SUCCESS(rv, rv);
diff --git a/caps/nsScriptSecurityManager.cpp b/caps/nsScriptSecurityManager.cpp
index 68ddbf5cb1d8..99742118c8ee 100644
--- a/caps/nsScriptSecurityManager.cpp
+++ b/caps/nsScriptSecurityManager.cpp
@@ -938,7 +938,7 @@ nsresult nsScriptSecurityManager::CheckLoadURIFlags(
         }
 
         auto& remoteType = dom::ContentChild::GetSingleton()->GetRemoteType();
-        if (remoteType == PRIVILEGEDABOUT_REMOTE_TYPE) {
+        if (remoteType.EqualsLiteral(PRIVILEGEDABOUT_REMOTE_TYPE)) {
           return NS_OK;
         }
       }
diff --git a/docshell/base/BrowsingContext.cpp b/docshell/base/BrowsingContext.cpp
index 84026f2bcadb..e37733bea7c1 100644
--- a/docshell/base/BrowsingContext.cpp
+++ b/docshell/base/BrowsingContext.cpp
@@ -1047,8 +1047,9 @@ bool BrowsingContext::CrossOriginIsolated() {
              nsILoadInfo::
                  OPENER_POLICY_SAME_ORIGIN_EMBEDDER_POLICY_REQUIRE_CORP &&
          XRE_IsContentProcess() &&
-         StringBeginsWith(ContentChild::GetSingleton()->GetRemoteType(),
-                          WITH_COOP_COEP_REMOTE_TYPE_PREFIX);
+         StringBeginsWith(
+             ContentChild::GetSingleton()->GetRemoteType(),
+             NS_LITERAL_STRING_FROM_CSTRING(WITH_COOP_COEP_REMOTE_TYPE_PREFIX));
 }
 
 BrowsingContext::~BrowsingContext() {
diff --git a/docshell/base/CanonicalBrowsingContext.cpp b/docshell/base/CanonicalBrowsingContext.cpp
index afc6d2f845e1..6fb0336a9456 100644
--- a/docshell/base/CanonicalBrowsingContext.cpp
+++ b/docshell/base/CanonicalBrowsingContext.cpp
@@ -94,11 +94,11 @@ ContentParent* CanonicalBrowsingContext::GetContentParent() const {
   return cpm->GetContentProcessById(ContentParentId(mProcessId));
 }
 
-void CanonicalBrowsingContext::GetCurrentRemoteType(nsACString& aRemoteType,
+void CanonicalBrowsingContext::GetCurrentRemoteType(nsAString& aRemoteType,
                                                     ErrorResult& aRv) const {
   // If we're in the parent process, dump out the void string.
   if (mProcessId == 0) {
-    aRemoteType = NOT_REMOTE_TYPE;
+    aRemoteType.Assign(VoidString());
     return;
   }
 
@@ -108,7 +108,7 @@ void CanonicalBrowsingContext::GetCurrentRemoteType(nsACString& aRemoteType,
     return;
   }
 
-  aRemoteType = cp->GetRemoteType();
+  aRemoteType.Assign(cp->GetRemoteType());
 }
 
 void CanonicalBrowsingContext::SetOwnerProcessId(uint64_t aProcessId) {
@@ -822,7 +822,7 @@ CanonicalBrowsingContext::PendingRemotenessChange::~PendingRemotenessChange() {
 }
 
 RefPtr<CanonicalBrowsingContext::RemotenessPromise>
-CanonicalBrowsingContext::ChangeRemoteness(const nsACString& aRemoteType,
+CanonicalBrowsingContext::ChangeRemoteness(const nsAString& aRemoteType,
                                            uint64_t aPendingSwitchId,
                                            bool aReplaceBrowsingContext,
                                            uint64_t aSpecificGroupId) {
diff --git a/docshell/base/CanonicalBrowsingContext.h b/docshell/base/CanonicalBrowsingContext.h
index 5fa55545d7d4..d62e583d53f3 100644
--- a/docshell/base/CanonicalBrowsingContext.h
+++ b/docshell/base/CanonicalBrowsingContext.h
@@ -59,7 +59,7 @@ class CanonicalBrowsingContext final : public BrowsingContext {
   uint64_t EmbedderProcessId() const { return mEmbedderProcessId; }
   ContentParent* GetContentParent() const;
 
-  void GetCurrentRemoteType(nsACString& aRemoteType, ErrorResult& aRv) const;
+  void GetCurrentRemoteType(nsAString& aRemoteType, ErrorResult& aRv) const;
 
   void SetOwnerProcessId(uint64_t aProcessId);
 
@@ -150,10 +150,10 @@ class CanonicalBrowsingContext final : public BrowsingContext {
   // Internal method to change which process a BrowsingContext is being loaded
   // in. The returned promise will resolve when the process switch is completed.
   //
-  // A NOT_REMOTE_TYPE aRemoteType argument will perform a process switch into
-  // the parent process, and the method will resolve with a null BrowserParent.
+  // A VoidString() aRemoteType argument will perform a process switch into the
+  // parent process, and the method will resolve with a null BrowserParent.
   using RemotenessPromise = MozPromise<RefPtr<BrowserParent>, nsresult, false>;
-  RefPtr<RemotenessPromise> ChangeRemoteness(const nsACString& aRemoteType,
+  RefPtr<RemotenessPromise> ChangeRemoteness(const nsAString& aRemoteType,
                                              uint64_t aPendingSwitchId,
                                              bool aReplaceBrowsingContext,
                                              uint64_t aSpecificGroupId);
diff --git a/dom/base/ChromeUtils.cpp b/dom/base/ChromeUtils.cpp
index baca12862dbd..9614b5d48430 100644
--- a/dom/base/ChromeUtils.cpp
+++ b/dom/base/ChromeUtils.cpp
@@ -795,7 +795,7 @@ already_AddRefed<Promise> ChromeUtils::RequestProcInfo(GlobalObject& aGlobal,
       global->EventTargetFor(TaskCategory::Performance);
 
   // Getting the parent proc info
-  mozilla::GetProcInfo(parentPid, 0, mozilla::ProcType::Browser, ""_ns)
+  mozilla::GetProcInfo(parentPid, 0, mozilla::ProcType::Browser, u""_ns)
       ->Then(
           target, __func__,
           [target, domPromise, parentPid](ProcInfo aParentInfo) {
@@ -809,7 +809,7 @@ already_AddRefed<Promise> ChromeUtils::RequestProcInfo(GlobalObject& aGlobal,
                   if (!aGeckoProcess->GetChildProcessHandle()) {
                     return;
                   }
-                  nsAutoCString origin;
+                  nsAutoString origin;
                   base::ProcessId childPid =
                       base::GetProcId(aGeckoProcess->GetChildProcessHandle());
                   int32_t childId = 0;
@@ -832,42 +832,50 @@ already_AddRefed<Promise> ChromeUtils::RequestProcInfo(GlobalObject& aGlobal,
                       // Converting the remoteType into a ProcType.
                       // Ideally, the remoteType should be strongly typed
                       // upstream, this would make the conversion less brittle.
-                      nsAutoCString remoteType(contentParent->GetRemoteType());
+                      nsAutoString remoteType(contentParent->GetRemoteType());
                       if (StringBeginsWith(remoteType,
-                                           FISSION_WEB_REMOTE_TYPE)) {
+                                           NS_LITERAL_STRING_FROM_CSTRING(
+                                               FISSION_WEB_REMOTE_TYPE))) {
                         // WARNING: Do not change the order, as
                         // `DEFAULT_REMOTE_TYPE` is a prefix of
                         // `FISSION_WEB_REMOTE_TYPE`.
                         type = mozilla::ProcType::WebIsolated;
-                      } else if (StringBeginsWith(remoteType,
-                                                  DEFAULT_REMOTE_TYPE)) {
+                      } else if (StringBeginsWith(
+                                     remoteType, NS_LITERAL_STRING_FROM_CSTRING(
+                                                     DEFAULT_REMOTE_TYPE))) {
                         type = mozilla::ProcType::Web;
-                      } else if (remoteType == FILE_REMOTE_TYPE) {
+                      } else if (remoteType.EqualsLiteral(FILE_REMOTE_TYPE)) {
                         type = mozilla::ProcType::File;
-                      } else if (remoteType == EXTENSION_REMOTE_TYPE) {
+                      } else if (remoteType.EqualsLiteral(
+                                     EXTENSION_REMOTE_TYPE)) {
                         type = mozilla::ProcType::Extension;
-                      } else if (remoteType == PRIVILEGEDABOUT_REMOTE_TYPE) {
+                      } else if (remoteType.EqualsLiteral(
+                                     PRIVILEGEDABOUT_REMOTE_TYPE)) {
                         type = mozilla::ProcType::PrivilegedAbout;
-                      } else if (remoteType == PRIVILEGEDMOZILLA_REMOTE_TYPE) {
+                      } else if (remoteType.EqualsLiteral(
+                                     PRIVILEGEDMOZILLA_REMOTE_TYPE)) {
                         type = mozilla::ProcType::PrivilegedMozilla;
                       } else if (StringBeginsWith(
                                      remoteType,
-                                     WITH_COOP_COEP_REMOTE_TYPE_PREFIX)) {
+                                     NS_LITERAL_STRING_FROM_CSTRING(
+                                         WITH_COOP_COEP_REMOTE_TYPE_PREFIX))) {
                         type = mozilla::ProcType::WebCOOPCOEP;
-                      } else if (remoteType == LARGE_ALLOCATION_REMOTE_TYPE) {
+                      } else if (remoteType.EqualsLiteral(
+                                     LARGE_ALLOCATION_REMOTE_TYPE)) {
                         type = mozilla::ProcType::WebLargeAllocation;
-                      } else if (remoteType == PREALLOC_REMOTE_TYPE) {
+                      } else if (remoteType.EqualsLiteral(
+                                     PREALLOC_REMOTE_TYPE)) {
                         type = mozilla::ProcType::Preallocated;
                       } else {
                         MOZ_CRASH("Unknown remoteType");
                       }
 
                       // By convention, everything after '=' is the origin.
-                      nsACString::const_iterator cursor;
-                      nsACString::const_iterator end;
+                      nsAString::const_iterator cursor;
+                      nsAString::const_iterator end;
                       remoteType.BeginReading(cursor);
                       remoteType.EndReading(end);
-                      if (FindCharInReadable('=', cursor, end)) {
+                      if (FindCharInReadable(u'=', cursor, end)) {
                         origin = Substring(++cursor, end);
                       }
                       childId = contentParent->ChildID();
diff --git a/dom/base/MessageManagerGlobal.h b/dom/base/MessageManagerGlobal.h
index 7e445e5bee38..16e6e00cd165 100644
--- a/dom/base/MessageManagerGlobal.h
+++ b/dom/base/MessageManagerGlobal.h
@@ -75,7 +75,7 @@ class MessageManagerGlobal {
     return mMessageManager->GetProcessMessageManager(aError);
   }
 
-  void GetRemoteType(nsACString& aRemoteType, mozilla::ErrorResult& aError) {
+  void GetRemoteType(nsAString& aRemoteType, mozilla::ErrorResult& aError) {
     if (!mMessageManager) {
       aError.Throw(NS_ERROR_NOT_INITIALIZED);
       return;
diff --git a/dom/base/nsFrameLoader.cpp b/dom/base/nsFrameLoader.cpp
index 4ff0cbac2ee7..3f840fafee98 100644
--- a/dom/base/nsFrameLoader.cpp
+++ b/dom/base/nsFrameLoader.cpp
@@ -169,7 +169,7 @@ nsFrameLoader::nsFrameLoader(Element* aOwner, BrowsingContext* aBrowsingContext,
       mDetachedSubdocFrame(nullptr),
       mPendingSwitchID(0),
       mChildID(0),
-      mRemoteType(NOT_REMOTE_TYPE),
+      mRemoteType(VoidString()),
       mDepthTooGreat(false),
       mIsTopLevelContent(false),
       mDestroyCalled(false),
@@ -351,20 +351,17 @@ static bool InitialLoadIsRemote(Element* aOwner) {
 }
 
 static void GetInitialRemoteTypeAndProcess(Element* aOwner,
-                                           nsACString& aRemoteType,
+                                           nsAString& aRemoteType,
                                            uint64_t* aChildID) {
   MOZ_ASSERT(XRE_IsParentProcess());
   *aChildID = 0;
 
   // Check if there is an explicit `remoteType` attribute which we should use.
-  nsAutoString remoteType;
   bool hasRemoteType =
-      aOwner->GetAttr(kNameSpaceID_None, nsGkAtoms::RemoteType, remoteType);
-  if (!hasRemoteType || remoteType.IsEmpty()) {
+      aOwner->GetAttr(kNameSpaceID_None, nsGkAtoms::RemoteType, aRemoteType);
+  if (!hasRemoteType || aRemoteType.IsEmpty()) {
     hasRemoteType = false;
-    aRemoteType = DEFAULT_REMOTE_TYPE;
-  } else {
-    aRemoteType = NS_ConvertUTF16toUTF8(remoteType);
+    aRemoteType.AssignLiteral(DEFAULT_REMOTE_TYPE);
   }
 
   // Check if `sameProcessAsFrameLoader` was used to override the process.
@@ -531,7 +528,7 @@ void nsFrameLoader::LoadFrame(bool aOriginalSrc) {
   }
 }
 
-void nsFrameLoader::ConfigRemoteProcess(const nsACString& aRemoteType,
+void nsFrameLoader::ConfigRemoteProcess(const nsAString& aRemoteType,
                                         ContentParent* aContentParent) {
   MOZ_DIAGNOSTIC_ASSERT(IsRemoteFrame(), "Must be a remote frame");
   MOZ_DIAGNOSTIC_ASSERT(!mRemoteBrowser, "Must not have a browser yet");
diff --git a/dom/base/nsFrameLoader.h b/dom/base/nsFrameLoader.h
index 1bd4d736604d..74337525c5f3 100644
--- a/dom/base/nsFrameLoader.h
+++ b/dom/base/nsFrameLoader.h
@@ -398,7 +398,7 @@ class nsFrameLoader final : public nsStubMutationObserver,
   // `TryRemoteBrowser`, and a script blocker must be on the stack.
   //
   // |aContentParent|, if set, must have the remote type |aRemoteType|.
-  void ConfigRemoteProcess(const nsACString& aRemoteType,
+  void ConfigRemoteProcess(const nsAString& aRemoteType,
                            mozilla::dom::ContentParent* aContentParent);
 
   void MaybeNotifyCrashed(mozilla::dom::BrowsingContext* aBrowsingContext,
@@ -515,7 +515,7 @@ class nsFrameLoader final : public nsStubMutationObserver,
 
   RefPtr<mozilla::dom::TabListener> mSessionStoreListener;
 
-  nsCString mRemoteType;
+  nsString mRemoteType;
 
   bool mDepthTooGreat : 1;
   bool mIsTopLevelContent : 1;
diff --git a/dom/base/nsFrameMessageManager.cpp b/dom/base/nsFrameMessageManager.cpp
index 024566814b42..7673869803ba 100644
--- a/dom/base/nsFrameMessageManager.cpp
+++ b/dom/base/nsFrameMessageManager.cpp
@@ -152,7 +152,7 @@ NS_INTERFACE_MAP_END
 NS_IMPL_CYCLE_COLLECTING_ADDREF(nsFrameMessageManager)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(nsFrameMessageManager)
 
-void MessageManagerCallback::DoGetRemoteType(nsACString& aRemoteType,
+void MessageManagerCallback::DoGetRemoteType(nsAString& aRemoteType,
                                              ErrorResult& aError) const {
   aRemoteType.Truncate();
   mozilla::dom::ProcessMessageManager* parent = GetProcessMessageManager();
@@ -917,7 +917,7 @@ nsFrameMessageManager::GetProcessMessageManager(ErrorResult& aError) {
   return pmm.forget();
 }
 
-void nsFrameMessageManager::GetRemoteType(nsACString& aRemoteType,
+void nsFrameMessageManager::GetRemoteType(nsAString& aRemoteType,
                                           ErrorResult& aError) const {
   aRemoteType.Truncate();
   if (mCallback) {
diff --git a/dom/base/nsFrameMessageManager.h b/dom/base/nsFrameMessageManager.h
index 48fe72d70e36..75cb09040278 100644
--- a/dom/base/nsFrameMessageManager.h
+++ b/dom/base/nsFrameMessageManager.h
@@ -99,7 +99,7 @@ class MessageManagerCallback {
     return nullptr;
   }
 
-  virtual void DoGetRemoteType(nsACString& aRemoteType,
+  virtual void DoGetRemoteType(nsAString& aRemoteType,
                                ErrorResult& aError) const;
 
  protected:
@@ -178,7 +178,7 @@ class nsFrameMessageManager : public nsIMessageSender {
   }
   already_AddRefed<mozilla::dom::ProcessMessageManager>
   GetProcessMessageManager(mozilla::ErrorResult& aError);
-  void GetRemoteType(nsACString& aRemoteType,
+  void GetRemoteType(nsAString& aRemoteType,
                      mozilla::ErrorResult& aError) const;
 
   // SyncMessageSender
diff --git a/dom/chrome-webidl/BrowsingContext.webidl b/dom/chrome-webidl/BrowsingContext.webidl
index 0b35cc8fe8ac..f3252a11cd5d 100644
--- a/dom/chrome-webidl/BrowsingContext.webidl
+++ b/dom/chrome-webidl/BrowsingContext.webidl
@@ -136,7 +136,7 @@ interface CanonicalBrowsingContext : BrowsingContext {
   // synchronously create WindowGlobalParent. It can throw if somehow the
   // content process has died.
   [Throws]
-  readonly attribute UTF8String? currentRemoteType;
+  readonly attribute DOMString? currentRemoteType;
 
   readonly attribute WindowGlobalParent? embedderWindowGlobal;
 
diff --git a/dom/chrome-webidl/ChromeUtils.webidl b/dom/chrome-webidl/ChromeUtils.webidl
index 974123cc2683..2f7ab48e9c2e 100644
--- a/dom/chrome-webidl/ChromeUtils.webidl
+++ b/dom/chrome-webidl/ChromeUtils.webidl
@@ -555,7 +555,7 @@ dictionary ChildProcInfoDictionary {
   sequence<ThreadInfoDictionary> threads = [];
   // Firefox info
   unsigned long long ChildID = 0;
-  UTF8String origin = "";
+  DOMString origin = "";
   WebIDLProcType type = "web";
 };
 
diff --git a/dom/chrome-webidl/JSProcessActor.webidl b/dom/chrome-webidl/JSProcessActor.webidl
index ba944f95fc2b..eea710b4d6fc 100644
--- a/dom/chrome-webidl/JSProcessActor.webidl
+++ b/dom/chrome-webidl/JSProcessActor.webidl
@@ -46,7 +46,7 @@ dictionary ProcessActorOptions {
    * can prefix match remote type either `web` or `webIsolated`. If not passed,
    * all content processes are allowed to instantiate the actor.
    */
-  sequence<UTF8String> remoteTypes;
+  sequence<DOMString> remoteTypes;
 
   /** This fields are used for configuring individual sides of the actor. */
   ProcessActorSidedOptions parent;
diff --git a/dom/chrome-webidl/JSWindowActor.webidl b/dom/chrome-webidl/JSWindowActor.webidl
index fa66a6893b32..f23f0aa0af05 100644
--- a/dom/chrome-webidl/JSWindowActor.webidl
+++ b/dom/chrome-webidl/JSWindowActor.webidl
@@ -97,7 +97,7 @@ dictionary WindowActorOptions {
    * can prefix match remote type either `web` or `webIsolated`. If not passed,
    * all content processes are allowed to instantiate the actor.
    */
-  sequence<UTF8String> remoteTypes;
+  sequence<DOMString> remoteTypes;
 
   /**
    * An array of MessageManagerGroup values which restrict which type
diff --git a/dom/chrome-webidl/MessageManager.webidl b/dom/chrome-webidl/MessageManager.webidl
index 99d026f5d887..6c2fb5fda653 100644
--- a/dom/chrome-webidl/MessageManager.webidl
+++ b/dom/chrome-webidl/MessageManager.webidl
@@ -322,7 +322,7 @@ interface mixin MessageSenderMixin {
    * Otherwise, it is empty.
    */
   [Throws]
-  readonly attribute UTF8String remoteType;
+  readonly attribute DOMString remoteType;
 };
 
 [ChromeOnly, Exposed=Window]
diff --git a/dom/interfaces/base/nsIContentProcess.idl b/dom/interfaces/base/nsIContentProcess.idl
index 198bb093a6ec..6bc52faf923b 100644
--- a/dom/interfaces/base/nsIContentProcess.idl
+++ b/dom/interfaces/base/nsIContentProcess.idl
@@ -45,7 +45,7 @@ interface nsIContentProcessProvider : nsISupports
    * nsIContentProcessProvider.NEW_PROCESS to ask the caller to create a new
    * content process.
    */
-  int32_t provideProcess(in AUTF8String aType,
+  int32_t provideProcess(in AString aType,
                          in Array<nsIContentProcessInfo> aAliveProcesses,
                          in uint32_t aMaxCount);
 };
diff --git a/dom/ipc/ContentChild.cpp b/dom/ipc/ContentChild.cpp
index 8d9913e51529..a5ec5802ef26 100644
--- a/dom/ipc/ContentChild.cpp
+++ b/dom/ipc/ContentChild.cpp
@@ -1653,7 +1653,7 @@ mozilla::ipc::IPCResult ContentChild::RecvSetProcessSandbox(
   // Use the prefix to avoid URIs from Fission isolated processes.
   auto remoteTypePrefix = RemoteTypePrefix(GetRemoteType());
   CrashReporter::AnnotateCrashReport(CrashReporter::Annotation::RemoteType,
-                                     remoteTypePrefix);
+                                     NS_ConvertUTF16toUTF8(remoteTypePrefix));
 #endif /* MOZ_SANDBOX */
 
   return IPC_OK();
@@ -2568,36 +2568,38 @@ mozilla::ipc::IPCResult ContentChild::RecvAppInfo(
 }
 
 mozilla::ipc::IPCResult ContentChild::RecvRemoteType(
-    const nsCString& aRemoteType) {
-  if (!mRemoteType.IsVoid()) {
+    const nsString& aRemoteType) {
+  if (!DOMStringIsNull(mRemoteType)) {
     // Preallocated processes are type PREALLOC_REMOTE_TYPE; they can become
     // anything except a File: process.
     MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
             ("Changing remoteType of process %d from %s to %s", getpid(),
-             mRemoteType.get(), aRemoteType.get()));
+             NS_ConvertUTF16toUTF8(mRemoteType).get(),
+             NS_ConvertUTF16toUTF8(aRemoteType).get()));
     // prealloc->anything (but file) or web->web allowed
-    MOZ_RELEASE_ASSERT(aRemoteType != FILE_REMOTE_TYPE &&
-                       (mRemoteType == PREALLOC_REMOTE_TYPE ||
-                        (mRemoteType == DEFAULT_REMOTE_TYPE &&
-                         aRemoteType == DEFAULT_REMOTE_TYPE)));
+    MOZ_RELEASE_ASSERT(!aRemoteType.EqualsLiteral(FILE_REMOTE_TYPE) &&
+                       (mRemoteType.EqualsLiteral(PREALLOC_REMOTE_TYPE) ||
+                        (mRemoteType.EqualsLiteral(DEFAULT_REMOTE_TYPE) &&
+                         aRemoteType.EqualsLiteral(DEFAULT_REMOTE_TYPE))));
   } else {
     // Initial setting of remote type.  Either to 'prealloc' or the actual
     // final type (if we didn't use a preallocated process)
     MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
             ("Setting remoteType of process %d to %s", getpid(),
-             aRemoteType.get()));
+             NS_ConvertUTF16toUTF8(aRemoteType).get()));
   }
 
   // Update the process name so about:memory's process names are more obvious.
-  if (aRemoteType == FILE_REMOTE_TYPE) {
+  if (aRemoteType.EqualsLiteral(FILE_REMOTE_TYPE)) {
     SetProcessName(u"file:// Content"_ns);
-  } else if (aRemoteType == EXTENSION_REMOTE_TYPE) {
+  } else if (aRemoteType.EqualsLiteral(EXTENSION_REMOTE_TYPE)) {
     SetProcessName(u"WebExtensions"_ns);
-  } else if (aRemoteType == PRIVILEGEDABOUT_REMOTE_TYPE) {
+  } else if (aRemoteType.EqualsLiteral(PRIVILEGEDABOUT_REMOTE_TYPE)) {
     SetProcessName(u"Privileged Content"_ns);
-  } else if (aRemoteType == LARGE_ALLOCATION_REMOTE_TYPE) {
+  } else if (aRemoteType.EqualsLiteral(LARGE_ALLOCATION_REMOTE_TYPE)) {
     SetProcessName(u"Large Allocation Web Content"_ns);
-  } else if (RemoteTypePrefix(aRemoteType) == FISSION_WEB_REMOTE_TYPE) {
+  } else if (RemoteTypePrefix(aRemoteType)
+                 .EqualsLiteral(FISSION_WEB_REMOTE_TYPE)) {
     SetProcessName(u"Isolated Web Content"_ns);
   }
   // else "prealloc", "web" or "webCOOP+COEP" type -> "Web Content" already set
@@ -2609,7 +2611,7 @@ mozilla::ipc::IPCResult ContentChild::RecvRemoteType(
 
 // Call RemoteTypePrefix() on the result to remove URIs if you want to use this
 // for telemetry.
-const nsACString& ContentChild::GetRemoteType() const { return mRemoteType; }
+const nsAString& ContentChild::GetRemoteType() const { return mRemoteType; }
 
 mozilla::ipc::IPCResult ContentChild::RecvInitServiceWorkers(
     const ServiceWorkerConfiguration& aConfig) {
diff --git a/dom/ipc/ContentChild.h b/dom/ipc/ContentChild.h
index 03edaaf33df0..c1d821be5867 100644
--- a/dom/ipc/ContentChild.h
+++ b/dom/ipc/ContentChild.h
@@ -17,7 +17,6 @@
 #include "mozilla/dom/MediaControllerBinding.h"
 #include "mozilla/dom/PContentChild.h"
 #include "mozilla/dom/RemoteBrowser.h"
-#include "mozilla/dom/RemoteType.h"
 #include "mozilla/StaticPtr.h"
 #include "mozilla/ipc/InputStreamUtils.h"
 #include "mozilla/ipc/Shmem.h"
@@ -391,11 +390,11 @@ class ContentChild final : public PContentChild,
       const nsCString& UAName, const nsCString& ID, const nsCString& vendor,
       const nsCString& sourceURL, const nsCString& updateURL);
 
-  mozilla::ipc::IPCResult RecvRemoteType(const nsCString& aRemoteType);
+  mozilla::ipc::IPCResult RecvRemoteType(const nsString& aRemoteType);
 
   // Call RemoteTypePrefix() on the result to remove URIs if you want to use
   // this for telemetry.
-  const nsACString& GetRemoteType() const override;
+  const nsAString& GetRemoteType() const override;
 
   mozilla::ipc::IPCResult RecvInitServiceWorkers(
       const ServiceWorkerConfiguration& aConfig);
@@ -864,7 +863,7 @@ class ContentChild final : public PContentChild,
   AppInfo mAppInfo;
 
   bool mIsForBrowser;
-  nsCString mRemoteType = NOT_REMOTE_TYPE;
+  nsString mRemoteType = VoidString();
   bool mIsAlive;
   nsString mProcessName;
 
diff --git a/dom/ipc/ContentParent.cpp b/dom/ipc/ContentParent.cpp
index 395d7983788a..b65a8e1ce54e 100644
--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -492,7 +492,7 @@ ContentParentsMemoryReporter::CollectReports(
 // processes that are in the Preallocator cache (which would be type
 // 'prealloc'), and recycled processes ('web' and in the future
 // eTLD+1-locked) processes).
-nsClassHashtable<nsCStringHashKey, nsTArray<ContentParent*>>*
+nsClassHashtable<nsStringHashKey, nsTArray<ContentParent*>>*
     ContentParent::sBrowserContentParents;
 
 namespace {
@@ -570,13 +570,13 @@ ScriptableCPInfo::GetMessageManager(nsISupports** aMessenger) {
   return NS_OK;
 }
 
-ProcessID GetTelemetryProcessID(const nsACString& remoteType) {
+ProcessID GetTelemetryProcessID(const nsAString& remoteType) {
   // OOP WebExtensions run in a content process.
   // For Telemetry though we want to break out collected data from the
   // WebExtensions process into a separate bucket, to make sure we can analyze
   // it separately and avoid skewing normal content process metrics.
-  return remoteType == EXTENSION_REMOTE_TYPE ? ProcessID::Extension
-                                             : ProcessID::Content;
+  return remoteType.EqualsLiteral(EXTENSION_REMOTE_TYPE) ? ProcessID::Extension
+                                                         : ProcessID::Content;
 }
 
 }  // anonymous namespace
@@ -638,10 +638,11 @@ static const char* sObserverTopics[] = {
 // ContentParent then takes this process back within GetNewOrUsedBrowserProcess.
 /*static*/ RefPtr<ContentParent::LaunchPromise>
 ContentParent::PreallocateProcess() {
-  RefPtr<ContentParent> process = new ContentParent(PREALLOC_REMOTE_TYPE);
+  RefPtr<ContentParent> process =
+      new ContentParent(NS_LITERAL_STRING_FROM_CSTRING(PREALLOC_REMOTE_TYPE));
 
   MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
-          ("Preallocating process of type prealloc"));
+          ("Preallocating process of type " PREALLOC_REMOTE_TYPE));
   return process->LaunchSubprocessAsync(PROCESS_PRIORITY_PREALLOC);
 }
 
@@ -687,7 +688,7 @@ void ContentParent::ShutDown() {
 }
 
 /*static*/
-uint32_t ContentParent::GetPoolSize(const nsACString& aContentProcessType) {
+uint32_t ContentParent::GetPoolSize(const nsAString& aContentProcessType) {
   if (!sBrowserContentParents) {
     return 0;
   }
@@ -699,17 +700,17 @@ uint32_t ContentParent::GetPoolSize(const nsACString& aContentProcessType) {
 }
 
 /*static*/ nsTArray<ContentParent*>& ContentParent::GetOrCreatePool(
-    const nsACString& aContentProcessType) {
+    const nsAString& aContentProcessType) {
   if (!sBrowserContentParents) {
     sBrowserContentParents =
-        new nsClassHashtable<nsCStringHashKey, nsTArray<ContentParent*>>;
+        new nsClassHashtable<nsStringHashKey, nsTArray<ContentParent*>>;
   }
 
   return *sBrowserContentParents->LookupOrAdd(aContentProcessType);
 }
 
-const nsDependentCSubstring RemoteTypePrefix(
-    const nsACString& aContentProcessType) {
+const nsDependentSubstring RemoteTypePrefix(
+    const nsAString& aContentProcessType) {
   // The suffix after a `=` in a remoteType is dynamic, and used to control the
   // process pool to use.
   int32_t equalIdx = aContentProcessType.FindChar(L'=');
@@ -719,26 +720,28 @@ const nsDependentCSubstring RemoteTypePrefix(
   return StringHead(aContentProcessType, equalIdx);
 }
 
-bool IsWebRemoteType(const nsACString& aContentProcessType) {
+bool IsWebRemoteType(const nsAString& aContentProcessType) {
   // Note: matches webIsolated as well as web (and webLargeAllocation, and
   // webCOOP+COEP)
-  return StringBeginsWith(aContentProcessType, DEFAULT_REMOTE_TYPE);
+  return StringBeginsWith(aContentProcessType,
+                          NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE));
 }
 
-bool IsWebCoopCoepRemoteType(const nsACString& aContentProcessType) {
-  return StringBeginsWith(aContentProcessType,
-                          WITH_COOP_COEP_REMOTE_TYPE_PREFIX);
+bool IsWebCoopCoepRemoteType(const nsAString& aContentProcessType) {
+  return StringBeginsWith(
+      aContentProcessType,
+      NS_LITERAL_STRING_FROM_CSTRING(WITH_COOP_COEP_REMOTE_TYPE_PREFIX));
 }
 
 /*static*/
 uint32_t ContentParent::GetMaxProcessCount(
-    const nsACString& aContentProcessType) {
+    const nsAString& aContentProcessType) {
   // Max process count is based only on the prefix.
-  const nsDependentCSubstring processTypePrefix =
+  const nsDependentSubstring processTypePrefix =
       RemoteTypePrefix(aContentProcessType);
 
   // Check for the default remote type of "web", as it uses different prefs.
-  if (processTypePrefix == DEFAULT_REMOTE_TYPE) {
+  if (processTypePrefix.EqualsLiteral(DEFAULT_REMOTE_TYPE)) {
     return GetMaxWebProcessCount();
   }
 
@@ -746,7 +749,7 @@ uint32_t ContentParent::GetMaxProcessCount(
   // used as a fallback, as it is intended to control the number of "web"
   // content processes, checked in `mozilla::GetMaxWebProcessCount()`.
   nsAutoCString processCountPref("dom.ipc.processCount.");
-  processCountPref.Append(processTypePrefix);
+  AppendUTF16toUTF8(processTypePrefix, processCountPref);
 
   int32_t maxContentParents = Preferences::GetInt(processCountPref.get(), 1);
   if (maxContentParents < 1) {
@@ -758,7 +761,7 @@ uint32_t ContentParent::GetMaxProcessCount(
 
 /*static*/
 bool ContentParent::IsMaxProcessCountReached(
-    const nsACString& aContentProcessType) {
+    const nsAString& aContentProcessType) {
   return GetPoolSize(aContentProcessType) >=
          GetMaxProcessCount(aContentProcessType);
 }
@@ -778,9 +781,10 @@ void ContentParent::ReleaseCachedProcesses() {
     nsTArray<ContentParent*>* contentParents = iter.Data().get();
     num += contentParents->Length();
     for (auto* cp : *contentParents) {
-      MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
-              ("%s: %zu processes", cp->mRemoteType.get(),
-               contentParents->Length()));
+      MOZ_LOG(
+          ContentParent::GetLog(), LogLevel::Debug,
+          ("%s: %zu processes", NS_ConvertUTF16toUTF8(cp->mRemoteType).get(),
+           contentParents->Length()));
       break;
     }
   }
@@ -796,12 +800,13 @@ void ContentParent::ReleaseCachedProcesses() {
     for (auto* cp : *contentParents) {
       if (cp->ManagedPBrowserParent().Count() == 0 &&
           !cp->HasActiveWorkerOrJSPlugin() &&
-          cp->mRemoteType == DEFAULT_REMOTE_TYPE) {
+          cp->mRemoteType.EqualsLiteral(DEFAULT_REMOTE_TYPE)) {
         toRelease.AppendElement(cp);
       } else {
         MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
                 ("  Skipping %p (%s), count %d, HasActiveWorkerOrJSPlugin %d",
-                 cp, cp->mRemoteType.get(), cp->ManagedPBrowserParent().Count(),
+                 cp, NS_ConvertUTF16toUTF8(cp->mRemoteType).get(),
+                 cp->ManagedPBrowserParent().Count(),
                  cp->HasActiveWorkerOrJSPlugin()));
       }
     }
@@ -809,7 +814,8 @@ void ContentParent::ReleaseCachedProcesses() {
 
   for (auto* cp : toRelease) {
     MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
-            ("  Shutdown %p (%s)", cp, cp->mRemoteType.get()));
+            ("  Shutdown %p (%s)", cp,
+             NS_ConvertUTF16toUTF8(cp->mRemoteType).get()));
     PreallocatedProcessManager::Erase(cp);
     // Start a soft shutdown.
     cp->ShutDownProcess(SEND_SHUTDOWN_MESSAGE);
@@ -857,7 +863,7 @@ already_AddRefed<ContentParent> ContentParent::MinTabSelect(
 
 /*static*/
 already_AddRefed<ContentParent> ContentParent::GetUsedBrowserProcess(
-    const nsACString& aRemoteType, nsTArray<ContentParent*>& aContentParents,
+    const nsAString& aRemoteType, nsTArray<ContentParent*>& aContentParents,
     uint32_t aMaxContentParents, bool aPreferUsed) {
 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
   AutoRestore ar(sInProcessSelector);
@@ -896,7 +902,7 @@ already_AddRefed<ContentParent> ContentParent::GetUsedBrowserProcess(
       MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
               ("GetUsedProcess: Reused process %p (%u) for %s", retval.get(),
                (unsigned int)retval->ChildID(),
-               PromiseFlatCString(aRemoteType).get()));
+               NS_ConvertUTF16toUTF8(aRemoteType).get()));
       retval->AssertAlive();
       return retval.forget();
     }
@@ -909,7 +915,7 @@ already_AddRefed<ContentParent> ContentParent::GetUsedBrowserProcess(
       MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
               ("GetUsedProcess: Reused random process %p (%d) for %s",
                random.get(), (unsigned int)random->ChildID(),
-               PromiseFlatCString(aRemoteType).get()));
+               NS_ConvertUTF16toUTF8(aRemoteType).get()));
       random->AssertAlive();
       return random.forget();
     }
@@ -921,8 +927,8 @@ already_AddRefed<ContentParent> ContentParent::GetUsedBrowserProcess(
   // try to reuse a process that is being shut down.
   RefPtr<ContentParent> p;
   bool preallocated = false;
-  if (aRemoteType != FILE_REMOTE_TYPE &&
-      aRemoteType != EXTENSION_REMOTE_TYPE &&  // Bug 1638119
+  if (!aRemoteType.EqualsLiteral(FILE_REMOTE_TYPE) &&
+      !aRemoteType.EqualsLiteral(EXTENSION_REMOTE_TYPE) &&  // Bug 1638119
       (p = PreallocatedProcessManager::Take(aRemoteType)) &&
       !p->mShutdownPending) {
     p->AssertAlive();
@@ -930,7 +936,7 @@ already_AddRefed<ContentParent> ContentParent::GetUsedBrowserProcess(
     // p may be a preallocated process, or (if not PREALLOC_REMOTE_TYPE)
     // a perviously-used process that's being recycled.  Currently this is
     // only done for short-duration web (DEFAULT_REMOTE_TYPE) processes
-    preallocated = p->mRemoteType == PREALLOC_REMOTE_TYPE;
+    preallocated = p->mRemoteType.EqualsLiteral(PREALLOC_REMOTE_TYPE);
     // For pre-allocated process we have not set the opener yet.
 #ifdef MOZ_GECKO_PROFILER
     if (profiler_thread_is_being_profiled()) {
@@ -945,7 +951,7 @@ already_AddRefed<ContentParent> ContentParent::GetUsedBrowserProcess(
     MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
             ("Adopted %s process %p for type %s",
              preallocated ? "preallocated" : "reused web", p.get(),
-             PromiseFlatCString(aRemoteType).get()));
+             NS_ConvertUTF16toUTF8(aRemoteType).get()));
     p->mActivateTS = TimeStamp::Now();
     p->AddToPool(aContentParents);
     if (preallocated) {
@@ -965,8 +971,8 @@ already_AddRefed<ContentParent> ContentParent::GetUsedBrowserProcess(
       }
     } else {
       // we only allow "web" to "web" for security reasons
-      MOZ_RELEASE_ASSERT(p->mRemoteType == DEFAULT_REMOTE_TYPE &&
-                         aRemoteType == DEFAULT_REMOTE_TYPE);
+      MOZ_RELEASE_ASSERT(p->mRemoteType.EqualsLiteral(DEFAULT_REMOTE_TYPE) &&
+                         aRemoteType.EqualsLiteral(DEFAULT_REMOTE_TYPE));
     }
     return p.forget();
   }
@@ -976,22 +982,25 @@ already_AddRefed<ContentParent> ContentParent::GetUsedBrowserProcess(
 
 /*static*/
 already_AddRefed<ContentParent>
-ContentParent::GetNewOrUsedLaunchingBrowserProcess(
-    Element* aFrameElement, const nsACString& aRemoteType,
-    ProcessPriority aPriority, bool aPreferUsed) {
+ContentParent::GetNewOrUsedLaunchingBrowserProcess(Element* aFrameElement,
+                                                   const nsAString& aRemoteType,
+                                                   ProcessPriority aPriority,
+                                                   bool aPreferUsed) {
   MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
           ("GetNewOrUsedProcess for type %s",
-           PromiseFlatCString(aRemoteType).get()));
+           NS_ConvertUTF16toUTF8(aRemoteType).get()));
   nsTArray<ContentParent*>& contentParents = GetOrCreatePool(aRemoteType);
   uint32_t maxContentParents = GetMaxProcessCount(aRemoteType);
-  // We never want to re-use Large-Allocation processes.
-  if (aRemoteType == LARGE_ALLOCATION_REMOTE_TYPE &&
-      contentParents.Length() >= maxContentParents) {
+  if (aRemoteType.EqualsLiteral(
+          LARGE_ALLOCATION_REMOTE_TYPE)  // We never want to re-use
+                                         // Large-Allocation processes.
+      && contentParents.Length() >= maxContentParents) {
     MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
             ("GetNewOrUsedProcess: returning Large Used process"));
-    return GetNewOrUsedLaunchingBrowserProcess(aFrameElement,
-                                               DEFAULT_REMOTE_TYPE, aPriority,
-                                               /*aPreferUsed =*/false);
+    return GetNewOrUsedLaunchingBrowserProcess(
+        aFrameElement, NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE),
+        aPriority,
+        /*aPreferUsed =*/false);
   }
 
   // Let's try and reuse an existing process.
@@ -1012,7 +1021,7 @@ ContentParent::GetNewOrUsedLaunchingBrowserProcess(
   // The life cycle will be set to `LifecycleState::LAUNCHING`.
   MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
           ("Launching new process immediately for type %s",
-           PromiseFlatCString(aRemoteType).get()));
+           NS_ConvertUTF16toUTF8(aRemoteType).get()));
 
   contentParent = new ContentParent(aRemoteType);
   if (!contentParent->BeginSubprocessLaunch(aPriority)) {
@@ -1039,7 +1048,7 @@ ContentParent::GetNewOrUsedLaunchingBrowserProcess(
 /*static*/
 RefPtr<ContentParent::LaunchPromise>
 ContentParent::GetNewOrUsedBrowserProcessAsync(Element* aFrameElement,
-                                               const nsACString& aRemoteType,
+                                               const nsAString& aRemoteType,
                                                ProcessPriority aPriority,
                                                bool aPreferUsed) {
   // Obtain a `ContentParent` launched asynchronously.
@@ -1054,7 +1063,7 @@ ContentParent::GetNewOrUsedBrowserProcessAsync(Element* aFrameElement,
 
 /*static*/
 already_AddRefed<ContentParent> ContentParent::GetNewOrUsedBrowserProcess(
-    Element* aFrameElement, const nsACString& aRemoteType,
+    Element* aFrameElement, const nsAString& aRemoteType,
     ProcessPriority aPriority, bool aPreferUsed) {
   RefPtr<ContentParent> contentParent = GetNewOrUsedLaunchingBrowserProcess(
       aFrameElement, aRemoteType, aPriority, aPreferUsed);
@@ -1303,7 +1312,7 @@ mozilla::ipc::IPCResult ContentParent::RecvLaunchRDDProcess(
 /*static*/
 already_AddRefed<RemoteBrowser> ContentParent::CreateBrowser(
     const TabContext& aContext, Element* aFrameElement,
-    const nsACString& aRemoteType, BrowsingContext* aBrowsingContext,
+    const nsAString& aRemoteType, BrowsingContext* aBrowsingContext,
     ContentParent* aOpenerContentParent) {
   AUTO_PROFILER_LABEL("ContentParent::CreateBrowser", OTHER);
 
@@ -1311,9 +1320,9 @@ already_AddRefed<RemoteBrowser> ContentParent::CreateBrowser(
     return nullptr;
   }
 
-  nsAutoCString remoteType(aRemoteType);
+  nsAutoString remoteType(aRemoteType);
   if (remoteType.IsEmpty()) {
-    remoteType = DEFAULT_REMOTE_TYPE;
+    remoteType.AssignLiteral(DEFAULT_REMOTE_TYPE);
   }
 
   ProcessPriority initialPriority = GetInitialProcessPriority(aFrameElement);
@@ -1471,7 +1480,7 @@ void ContentParent::BroadcastFontListChanged() {
   }
 }
 
-const nsACString& ContentParent::GetRemoteType() const { return mRemoteType; }
+const nsAString& ContentParent::GetRemoteType() const { return mRemoteType; }
 
 void ContentParent::Init() {
   nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
@@ -1931,7 +1940,7 @@ void ContentParent::ActorDealloc() { mSelfRef = nullptr; }
 bool ContentParent::TryToRecycle() {
   // We can only do this if we have a separate cache for recycled
   // 'web' processes, and handle them differently than webIsolated ones
-  if (mRemoteType != DEFAULT_REMOTE_TYPE) {
+  if (!mRemoteType.EqualsLiteral(DEFAULT_REMOTE_TYPE)) {
     return false;
   }
   // This life time check should be replaced by a memory health check (memory
@@ -2017,12 +2026,13 @@ bool ContentParent::ShouldKeepProcessAlive() {
 
   nsAutoCString keepAlivePref("dom.ipc.keepProcessesAlive.");
 
-  if (StringBeginsWith(mRemoteType, FISSION_WEB_REMOTE_TYPE) &&
+  if (StringBeginsWith(mRemoteType, NS_LITERAL_STRING_FROM_CSTRING(
+                                        FISSION_WEB_REMOTE_TYPE)) &&
       xpc::IsInAutomation()) {
     keepAlivePref.Append(FISSION_WEB_REMOTE_TYPE);
     keepAlivePref.AppendLiteral(".perOrigin");
   } else {
-    keepAlivePref.Append(mRemoteType);
+    keepAlivePref.Append(NS_ConvertUTF16toUTF8(mRemoteType));
   }
   if (NS_FAILED(
           Preferences::GetInt(keepAlivePref.get(), &processesToKeepAlive))) {
@@ -2143,7 +2153,7 @@ TestShellParent* ContentParent::GetTestShellSingleton() {
 void ContentParent::AppendDynamicSandboxParams(
     std::vector<std::string>& aArgs) {
   // For file content processes
-  if (GetRemoteType() == FILE_REMOTE_TYPE) {
+  if (GetRemoteType().EqualsLiteral(FILE_REMOTE_TYPE)) {
     MacSandboxInfo::AppendFileAccessParam(aArgs, true);
   }
 }
@@ -2451,7 +2461,7 @@ RefPtr<ContentParent::LaunchPromise> ContentParent::LaunchSubprocessAsync(
       });
 }
 
-ContentParent::ContentParent(const nsACString& aRemoteType, int32_t aJSPluginID)
+ContentParent::ContentParent(const nsAString& aRemoteType, int32_t aJSPluginID)
     : mSelfRef(nullptr),
       mSubprocess(nullptr),
       mLaunchTS(TimeStamp::Now()),
@@ -2500,7 +2510,7 @@ ContentParent::ContentParent(const nsACString& aRemoteType, int32_t aJSPluginID)
 #endif
 
   NS_ASSERTION(NS_IsMainThread(), "Wrong thread!");
-  bool isFile = mRemoteType == FILE_REMOTE_TYPE;
+  bool isFile = mRemoteType.EqualsLiteral(FILE_REMOTE_TYPE);
   mSubprocess = new GeckoChildProcessHost(GeckoProcessType_Content, isFile);
   MOZ_LOG(ContentParent::GetLog(), LogLevel::Verbose,
           ("CreateSubprocess: ContentParent %p mSubprocess %p handle %" PRIuPTR,
@@ -2807,7 +2817,7 @@ bool ContentParent::InitInternal(ProcessPriority aInitialPriority) {
 #  ifdef XP_LINUX
   if (shouldSandbox) {
     MOZ_ASSERT(!mSandboxBroker);
-    bool isFileProcess = mRemoteType == FILE_REMOTE_TYPE;
+    bool isFileProcess = mRemoteType.EqualsLiteral(FILE_REMOTE_TYPE);
     UniquePtr<SandboxBroker::Policy> policy =
         sSandboxBrokerPolicyFactory->GetContentPolicy(Pid(), isFileProcess);
     if (policy) {
@@ -3191,8 +3201,8 @@ ContentParent::GetName(nsAString& aName) {
 NS_IMETHODIMP
 ContentParent::GetState(nsIPropertyBag** aResult) {
   auto props = MakeRefPtr<nsHashPropertyBag>();
-  props->SetPropertyAsACString(u"remoteTypePrefix"_ns,
-                               RemoteTypePrefix(mRemoteType));
+  props->SetPropertyAsAString(u"remoteTypePrefix"_ns,
+                              RemoteTypePrefix(mRemoteType));
   *aResult = props.forget().downcast<nsIWritablePropertyBag>().take();
   return NS_OK;
 }
@@ -5228,7 +5238,7 @@ mozilla::ipc::IPCResult ContentParent::RecvCreateWindowInDifferentProcess(
   // If we have enough data, check the schemes of the loader and loadee
   // to make sure they make sense.
   if (aURIToLoad && aURIToLoad->SchemeIs("file") &&
-      GetRemoteType() != FILE_REMOTE_TYPE &&
+      !GetRemoteType().EqualsLiteral(FILE_REMOTE_TYPE) &&
       Preferences::GetBool("browser.tabs.remote.enforceRemoteTypeRestrictions",
                            false)) {
 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
diff --git a/dom/ipc/ContentParent.h b/dom/ipc/ContentParent.h
index 3639c661afa4..4efc42b57db7 100644
--- a/dom/ipc/ContentParent.h
+++ b/dom/ipc/ContentParent.h
@@ -11,7 +11,6 @@
 #include "mozilla/dom/ipc/IdType.h"
 #include "mozilla/dom/MediaSessionBinding.h"
 #include "mozilla/dom/RemoteBrowser.h"
-#include "mozilla/dom/RemoteType.h"
 #include "mozilla/dom/JSProcessActorParent.h"
 #include "mozilla/dom/ProcessActor.h"
 #include "mozilla/gfx/gfxVarReceiver.h"
@@ -50,6 +49,22 @@
 
 #define CHILD_PROCESS_SHUTDOWN_MESSAGE u"child-process-shutdown"_ns
 
+// These must match the similar ones in E10SUtils.jsm and ProcInfo.h.
+// Process names as reported by about:memory are defined in
+// ContentChild:RecvRemoteType.  Add your value there too or it will be called
+// "Web Content".
+#define PREALLOC_REMOTE_TYPE "prealloc"
+#define DEFAULT_REMOTE_TYPE "web"
+#define FILE_REMOTE_TYPE "file"
+#define EXTENSION_REMOTE_TYPE "extension"
+#define PRIVILEGEDABOUT_REMOTE_TYPE "privilegedabout"
+#define PRIVILEGEDMOZILLA_REMOTE_TYPE "privilegedmozilla"
+
+// These must start with the DEFAULT_REMOTE_TYPE above.
+#define FISSION_WEB_REMOTE_TYPE "webIsolated"
+#define WITH_COOP_COEP_REMOTE_TYPE_PREFIX "webCOOP+COEP="
+#define LARGE_ALLOCATION_REMOTE_TYPE "webLargeAllocation"
+
 class nsConsoleService;
 class nsIContentProcessInfo;
 class nsICycleCollectorLogSink;
@@ -164,11 +179,11 @@ class ContentParent final
   /** Shut down the content-process machinery. */
   static void ShutDown();
 
-  static uint32_t GetPoolSize(const nsACString& aContentProcessType);
+  static uint32_t GetPoolSize(const nsAString& aContentProcessType);
 
-  static uint32_t GetMaxProcessCount(const nsACString& aContentProcessType);
+  static uint32_t GetMaxProcessCount(const nsAString& aContentProcessType);
 
-  static bool IsMaxProcessCountReached(const nsACString& aContentProcessType);
+  static bool IsMaxProcessCountReached(const nsAString& aContentProcessType);
 
   static void ReleaseCachedProcesses();
 
@@ -188,12 +203,12 @@ class ContentParent final
    * 3. normal iframe
    */
   static RefPtr<ContentParent::LaunchPromise> GetNewOrUsedBrowserProcessAsync(
-      Element* aFrameElement, const nsACString& aRemoteType,
+      Element* aFrameElement, const nsAString& aRemoteType,
       hal::ProcessPriority aPriority =
           hal::ProcessPriority::PROCESS_PRIORITY_FOREGROUND,
       bool aPreferUsed = false);
   static already_AddRefed<ContentParent> GetNewOrUsedBrowserProcess(
-      Element* aFrameElement, const nsACString& aRemoteType,
+      Element* aFrameElement, const nsAString& aRemoteType,
       hal::ProcessPriority aPriority =
           hal::ProcessPriority::PROCESS_PRIORITY_FOREGROUND,
       bool aPreferUsed = false);
@@ -209,7 +224,7 @@ class ContentParent final
    * the process to be fully launched.
    */
   static already_AddRefed<ContentParent> GetNewOrUsedLaunchingBrowserProcess(
-      Element* aFrameElement, const nsACString& aRemoteType,
+      Element* aFrameElement, const nsAString& aRemoteType,
       hal::ProcessPriority aPriority =
           hal::ProcessPriority::PROCESS_PRIORITY_FOREGROUND,
       bool aPreferUsed = false);
@@ -235,7 +250,7 @@ class ContentParent final
    */
   static already_AddRefed<RemoteBrowser> CreateBrowser(
       const TabContext& aContext, Element* aFrameElement,
-      const nsACString& aRemoteType, BrowsingContext* aBrowsingContext,
+      const nsAString& aRemoteType, BrowsingContext* aBrowsingContext,
       ContentParent* aOpenerContentParent);
 
   static void GetAll(nsTArray<ContentParent*>& aArray);
@@ -246,9 +261,9 @@ class ContentParent final
 
   static void BroadcastFontListChanged();
 
-  const nsACString& GetRemoteType() const override;
+  const nsAString& GetRemoteType() const override;
 
-  virtual void DoGetRemoteType(nsACString& aRemoteType,
+  virtual void DoGetRemoteType(nsAString& aRemoteType,
                                ErrorResult& aError) const override {
     aRemoteType = GetRemoteType();
   }
@@ -708,7 +723,7 @@ class ContentParent final
    * removed from this list, but will still be in the sContentParents list for
    * the GetAll/GetAllEvenIfDead APIs.
    */
-  static nsClassHashtable<nsCStringHashKey, nsTArray<ContentParent*>>*
+  static nsClassHashtable<nsStringHashKey, nsTArray<ContentParent*>>*
       sBrowserContentParents;
   static UniquePtr<nsTArray<ContentParent*>> sPrivateContent;
   static UniquePtr<nsDataHashtable<nsUint32HashKey, ContentParent*>>
@@ -739,11 +754,11 @@ class ContentParent final
       const OriginAttributes& aOriginAttributes);
 
   explicit ContentParent(int32_t aPluginID)
-      : ContentParent(EmptyCString(), aPluginID) {}
-  explicit ContentParent(const nsACString& aRemoteType)
+      : ContentParent(EmptyString(), aPluginID) {}
+  explicit ContentParent(const nsAString& aRemoteType)
       : ContentParent(aRemoteType, nsFakePluginTag::NOT_JSPLUGIN) {}
 
-  ContentParent(const nsACString& aRemoteType, int32_t aPluginID);
+  ContentParent(const nsAString& aRemoteType, int32_t aPluginID);
 
   // Launch the subprocess and associated initialization.
   // Returns false if the process fails to start.
@@ -866,7 +881,7 @@ class ContentParent final
    * |aContentProcessType|.
    */
   static nsTArray<ContentParent*>& GetOrCreatePool(
-      const nsACString& aContentProcessType);
+      const nsAString& aContentProcessType);
 
   mozilla::ipc::IPCResult RecvInitBackground(
       Endpoint<mozilla::ipc::PBackgroundParent>&& aEndpoint);
@@ -1355,7 +1370,7 @@ class ContentParent final
  private:
   // Return an existing ContentParent if possible. Otherwise, `nullptr`.
   static already_AddRefed<ContentParent> GetUsedBrowserProcess(
-      const nsACString& aRemoteType, nsTArray<ContentParent*>& aContentParents,
+      const nsAString& aRemoteType, nsTArray<ContentParent*>& aContentParents,
       uint32_t aMaxContentParents, bool aPreferUsed);
 
   void AddToPool(nsTArray<ContentParent*>&);
@@ -1379,7 +1394,7 @@ class ContentParent final
 
   bool mIsAPreallocBlocker;  // We called AddBlocker for this ContentParent
 
-  nsCString mRemoteType;
+  nsString mRemoteType;
 
   ContentParentId mChildID;
   int32_t mGeolocationWatchID;
@@ -1528,13 +1543,13 @@ class ContentParent final
 NS_DEFINE_STATIC_IID_ACCESSOR(ContentParent, NS_CONTENTPARENT_IID)
 
 // This is the C++ version of remoteTypePrefix in E10SUtils.jsm.
-const nsDependentCSubstring RemoteTypePrefix(
-    const nsACString& aContentProcessType);
+const nsDependentSubstring RemoteTypePrefix(
+    const nsAString& aContentProcessType);
 
 // This is based on isWebRemoteType in E10SUtils.jsm.
-bool IsWebRemoteType(const nsACString& aContentProcessType);
+bool IsWebRemoteType(const nsAString& aContentProcessType);
 
-bool IsWebCoopCoepRemoteType(const nsACString& aContentProcessType);
+bool IsWebCoopCoepRemoteType(const nsAString& aContentProcessType);
 
 inline nsISupports* ToSupports(mozilla::dom::ContentParent* aContentParent) {
   return static_cast<nsIDOMProcessParent*>(aContentParent);
diff --git a/dom/ipc/InProcessChild.h b/dom/ipc/InProcessChild.h
index c90e9f7157d6..d6d0d6a29f30 100644
--- a/dom/ipc/InProcessChild.h
+++ b/dom/ipc/InProcessChild.h
@@ -10,7 +10,6 @@
 #include "mozilla/dom/PInProcessChild.h"
 #include "mozilla/dom/JSProcessActorChild.h"
 #include "mozilla/dom/ProcessActor.h"
-#include "mozilla/dom/RemoteType.h"
 #include "mozilla/StaticPtr.h"
 #include "nsIDOMProcessChild.h"
 
@@ -46,7 +45,7 @@ class InProcessChild final : public nsIDOMProcessChild,
   // |nullptr|.
   static IProtocol* ParentActorFor(IProtocol* aActor);
 
-  const nsACString& GetRemoteType() const override { return NOT_REMOTE_TYPE; }
+  const nsAString& GetRemoteType() const override { return VoidString(); }
 
  protected:
   already_AddRefed<JSActor> InitJSActor(JS::HandleObject aMaybeActor,
diff --git a/dom/ipc/InProcessParent.h b/dom/ipc/InProcessParent.h
index 6a4acc7e77ec..46ec01185248 100644
--- a/dom/ipc/InProcessParent.h
+++ b/dom/ipc/InProcessParent.h
@@ -10,7 +10,6 @@
 #include "mozilla/dom/PInProcessParent.h"
 #include "mozilla/dom/JSProcessActorParent.h"
 #include "mozilla/dom/ProcessActor.h"
-#include "mozilla/dom/RemoteType.h"
 #include "mozilla/StaticPtr.h"
 #include "nsIDOMProcessParent.h"
 
@@ -48,7 +47,7 @@ class InProcessParent final : public nsIDOMProcessParent,
   // |nullptr|.
   static IProtocol* ChildActorFor(IProtocol* aActor);
 
-  const nsACString& GetRemoteType() const override { return NOT_REMOTE_TYPE; };
+  const nsAString& GetRemoteType() const override { return VoidString(); };
 
  protected:
   already_AddRefed<JSActor> InitJSActor(JS::HandleObject aMaybeActor,
diff --git a/dom/ipc/PContent.ipdl b/dom/ipc/PContent.ipdl
index c0d933962b8d..a272b8275a48 100644
--- a/dom/ipc/PContent.ipdl
+++ b/dom/ipc/PContent.ipdl
@@ -259,7 +259,7 @@ struct JSWindowActorInfo
   // Observer notifications this actor listens to.
   nsCString[] observers;
   nsString[] matches;
-  nsCString[] remoteTypes;
+  nsString[] remoteTypes;
   nsString[] messageManagerGroups;
 };
 
@@ -272,7 +272,7 @@ struct JSProcessActorInfo
 
     // Observer notifications this actor listens to.
     nsCString[] observers;
-    nsCString[] remoteTypes;
+    nsString[] remoteTypes;
 };
 
 struct GMPAPITags
@@ -636,7 +636,7 @@ child:
     /**
      * Send the remote type associated with the content process.
      */
-    async RemoteType(nsCString aRemoteType);
+    async RemoteType(nsString aRemoteType);
 
     /**
      * Send ServiceWorkerRegistrationData to child process.
diff --git a/dom/ipc/PreallocatedProcessManager.cpp b/dom/ipc/PreallocatedProcessManager.cpp
index e0ee153c6f90..79695c9622ab 100644
--- a/dom/ipc/PreallocatedProcessManager.cpp
+++ b/dom/ipc/PreallocatedProcessManager.cpp
@@ -37,7 +37,7 @@ class PreallocatedProcessManagerImpl final : public nsIObserver {
   // See comments on PreallocatedProcessManager for these methods.
   void AddBlocker(ContentParent* aParent);
   void RemoveBlocker(ContentParent* aParent);
-  already_AddRefed<ContentParent> Take(const nsACString& aRemoteType);
+  already_AddRefed<ContentParent> Take(const nsAString& aRemoteType);
   bool Provide(ContentParent* aParent);
   void Erase(ContentParent* aParent);
 
@@ -190,17 +190,17 @@ void PreallocatedProcessManagerImpl::RereadPrefs() {
 }
 
 already_AddRefed<ContentParent> PreallocatedProcessManagerImpl::Take(
-    const nsACString& aRemoteType) {
+    const nsAString& aRemoteType) {
   if (!mEnabled || sShutdown) {
     return nullptr;
   }
   RefPtr<ContentParent> process;
-  if (aRemoteType == DEFAULT_REMOTE_TYPE) {
+  if (aRemoteType.EqualsLiteral(DEFAULT_REMOTE_TYPE)) {
     // we can recycle processes via Provide() for e10s only
     process = mPreallocatedE10SProcess.forget();
     if (process) {
       MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
-              ("Reuse web process %p", process.get()));
+              ("Reuse " DEFAULT_REMOTE_TYPE " process %p", process.get()));
     }
   }
   if (!process && !mPreallocatedProcesses.empty()) {
@@ -210,7 +210,7 @@ already_AddRefed<ContentParent> PreallocatedProcessManagerImpl::Take(
     // soon.
     AllocateOnIdle();
     MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
-            ("Use prealloc process %p", process.get()));
+            ("Use " PREALLOC_REMOTE_TYPE " process %p", process.get()));
   }
   if (process) {
     ProcessPriorityManager::SetProcessPriority(process,
@@ -220,14 +220,15 @@ already_AddRefed<ContentParent> PreallocatedProcessManagerImpl::Take(
 }
 
 bool PreallocatedProcessManagerImpl::Provide(ContentParent* aParent) {
-  MOZ_DIAGNOSTIC_ASSERT(aParent->GetRemoteType() == DEFAULT_REMOTE_TYPE);
+  MOZ_DIAGNOSTIC_ASSERT(
+      aParent->GetRemoteType().EqualsLiteral(DEFAULT_REMOTE_TYPE));
 
   // This will take the already-running process even if there's a
   // launch in progress; if that process hasn't been taken by the
   // time the launch completes, the new process will be shut down.
   if (mEnabled && !sShutdown && !mPreallocatedE10SProcess) {
     MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
-            ("Store for reuse web process %p", aParent));
+            ("Store for reuse " DEFAULT_REMOTE_TYPE " process %p", aParent));
     ProcessPriorityManager::SetProcessPriority(aParent,
                                                PROCESS_PRIORITY_BACKGROUND);
     mPreallocatedE10SProcess = aParent;
@@ -299,7 +300,8 @@ bool PreallocatedProcessManagerImpl::CanAllocate() {
   return mEnabled && sNumBlockers == 0 &&
          mPreallocatedProcesses.size() < mNumberPreallocs && !sShutdown &&
          (FissionAutostart() ||
-          !ContentParent::IsMaxProcessCountReached(DEFAULT_REMOTE_TYPE));
+          !ContentParent::IsMaxProcessCountReached(
+              NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE)));
 }
 
 void PreallocatedProcessManagerImpl::AllocateAfterDelay() {
@@ -400,11 +402,11 @@ PreallocatedProcessManager::GetPPMImpl() {
 }
 
 /* static */
-void PreallocatedProcessManager::AddBlocker(const nsACString& aRemoteType,
+void PreallocatedProcessManager::AddBlocker(const nsAString& aRemoteType,
                                             ContentParent* aParent) {
   MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
           ("AddBlocker: %s %p (sNumBlockers=%d)",
-           PromiseFlatCString(aRemoteType).get(), aParent,
+           NS_ConvertUTF16toUTF8(aRemoteType).get(), aParent,
            PreallocatedProcessManagerImpl::sNumBlockers));
   if (auto impl = GetPPMImpl()) {
     impl->AddBlocker(aParent);
@@ -412,11 +414,11 @@ void PreallocatedProcessManager::AddBlocker(const nsACString& aRemoteType,
 }
 
 /* static */
-void PreallocatedProcessManager::RemoveBlocker(const nsACString& aRemoteType,
+void PreallocatedProcessManager::RemoveBlocker(const nsAString& aRemoteType,
                                                ContentParent* aParent) {
   MOZ_LOG(ContentParent::GetLog(), LogLevel::Debug,
           ("RemoveBlocker: %s %p (sNumBlockers=%d)",
-           PromiseFlatCString(aRemoteType).get(), aParent,
+           NS_ConvertUTF16toUTF8(aRemoteType).get(), aParent,
            PreallocatedProcessManagerImpl::sNumBlockers));
   if (auto impl = GetPPMImpl()) {
     impl->RemoveBlocker(aParent);
@@ -425,7 +427,7 @@ void PreallocatedProcessManager::RemoveBlocker(const nsACString& aRemoteType,
 
 /* static */
 already_AddRefed<ContentParent> PreallocatedProcessManager::Take(
-    const nsACString& aRemoteType) {
+    const nsAString& aRemoteType) {
   if (auto impl = GetPPMImpl()) {
     return impl->Take(aRemoteType);
   }
diff --git a/dom/ipc/PreallocatedProcessManager.h b/dom/ipc/PreallocatedProcessManager.h
index ed70b516a168..a06c91eb8bd7 100644
--- a/dom/ipc/PreallocatedProcessManager.h
+++ b/dom/ipc/PreallocatedProcessManager.h
@@ -42,8 +42,8 @@ class PreallocatedProcessManager final {
    * background. To avoid that, the PreallocatedProcessManager won't start up
    * any processes while there is a blocker active.
    */
-  static void AddBlocker(const nsACString& aRemoteType, ContentParent* aParent);
-  static void RemoveBlocker(const nsACString& aRemoteType,
+  static void AddBlocker(const nsAString& aRemoteType, ContentParent* aParent);
+  static void RemoveBlocker(const nsAString& aRemoteType,
                             ContentParent* aParent);
 
   /**
@@ -56,7 +56,7 @@ class PreallocatedProcessManager final {
    * If we use a preallocated process, it will schedule the start of
    * another on Idle (AllocateOnIdle()).
    */
-  static already_AddRefed<ContentParent> Take(const nsACString& aRemoteType);
+  static already_AddRefed<ContentParent> Take(const nsAString& aRemoteType);
 
   /**
    * Cache a process (currently only DEFAULT_REMOTE_TYPE) for reuse later
diff --git a/dom/ipc/ProcessActor.h b/dom/ipc/ProcessActor.h
index f0b72382dbfb..cd2b9abe8a11 100644
--- a/dom/ipc/ProcessActor.h
+++ b/dom/ipc/ProcessActor.h
@@ -28,7 +28,7 @@ class ProcessActor : public JSActorManager {
       JSActorService* aActorSvc, const nsACString& aName,
       ErrorResult& aRv) final;
 
-  virtual const nsACString& GetRemoteType() const = 0;
+  virtual const nsAString& GetRemoteType() const = 0;
 };
 
 }  // namespace dom
diff --git a/dom/ipc/ProcessPriorityManager.cpp b/dom/ipc/ProcessPriorityManager.cpp
index a2ee913323e3..a4aaae307450 100644
--- a/dom/ipc/ProcessPriorityManager.cpp
+++ b/dom/ipc/ProcessPriorityManager.cpp
@@ -734,7 +734,7 @@ ProcessPriority ParticularProcessPriorityManager::CurrentPriority() {
 
 ProcessPriority ParticularProcessPriorityManager::ComputePriority() {
   if (!mActiveBrowserParents.IsEmpty() ||
-      mContentParent->GetRemoteType() == EXTENSION_REMOTE_TYPE ||
+      mContentParent->GetRemoteType().EqualsLiteral(EXTENSION_REMOTE_TYPE) ||
       mHoldsPlayingAudioWakeLock) {
     return PROCESS_PRIORITY_FOREGROUND;
   }
diff --git a/dom/ipc/RemoteType.h b/dom/ipc/RemoteType.h
deleted file mode 100644
index b79c97f8c9be..000000000000
--- a/dom/ipc/RemoteType.h
+++ /dev/null
@@ -1,32 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef mozilla_dom_RemoteType_h
-#define mozilla_dom_RemoteType_h
-
-#include "nsString.h"
-#include "nsReadableUtils.h"
-
-// These must match the similar ones in E10SUtils.jsm and ProcInfo.h.
-// Process names as reported by about:memory are defined in
-// ContentChild:RecvRemoteType.  Add your value there too or it will be called
-// "Web Content".
-#define PREALLOC_REMOTE_TYPE "prealloc"_ns
-#define DEFAULT_REMOTE_TYPE "web"_ns
-#define FILE_REMOTE_TYPE "file"_ns
-#define EXTENSION_REMOTE_TYPE "extension"_ns
-#define PRIVILEGEDABOUT_REMOTE_TYPE "privilegedabout"_ns
-#define PRIVILEGEDMOZILLA_REMOTE_TYPE "privilegedmozilla"_ns
-
-// These must start with the DEFAULT_REMOTE_TYPE above.
-#define FISSION_WEB_REMOTE_TYPE "webIsolated"_ns
-#define WITH_COOP_COEP_REMOTE_TYPE_PREFIX "webCOOP+COEP="_ns
-#define LARGE_ALLOCATION_REMOTE_TYPE "webLargeAllocation"_ns
-
-// Remote type value used to represent being non-remote.
-#define NOT_REMOTE_TYPE VoidCString()
-
-#endif  // mozilla_dom_RemoteType_h
diff --git a/dom/ipc/WindowGlobalActor.h b/dom/ipc/WindowGlobalActor.h
index 0957e67ffea0..5aa8eb74d5f8 100644
--- a/dom/ipc/WindowGlobalActor.h
+++ b/dom/ipc/WindowGlobalActor.h
@@ -40,7 +40,7 @@ class WindowGlobalActor : public JSActorManager {
       ErrorResult& aRv) final;
 
   virtual nsIURI* GetDocumentURI() = 0;
-  virtual const nsACString& GetRemoteType() = 0;
+  virtual const nsAString& GetRemoteType() = 0;
   virtual dom::BrowsingContext* BrowsingContext() = 0;
 
   static WindowGlobalInit BaseInitializer(
diff --git a/dom/ipc/WindowGlobalChild.cpp b/dom/ipc/WindowGlobalChild.cpp
index b1f446db4395..1e051dcbffed 100644
--- a/dom/ipc/WindowGlobalChild.cpp
+++ b/dom/ipc/WindowGlobalChild.cpp
@@ -359,7 +359,7 @@ mozilla::ipc::IPCResult WindowGlobalChild::RecvMakeFrameLocal(
 
   // Trigger a process switch into the current process.
   RemotenessOptions options;
-  options.mRemoteType = NOT_REMOTE_TYPE;
+  options.mRemoteType.Assign(VoidString());
   options.mPendingSwitchID.Construct(aPendingSwitchId);
   options.mSwitchingInProgressLoad = true;
   flo->ChangeRemoteness(options, IgnoreErrors());
@@ -573,12 +573,12 @@ void WindowGlobalChild::SetDocumentPrincipal(
   SendUpdateDocumentPrincipal(aNewDocumentPrincipal);
 }
 
-const nsACString& WindowGlobalChild::GetRemoteType() {
+const nsAString& WindowGlobalChild::GetRemoteType() {
   if (XRE_IsContentProcess()) {
     return ContentChild::GetSingleton()->GetRemoteType();
   }
 
-  return NOT_REMOTE_TYPE;
+  return VoidString();
 }
 
 already_AddRefed<JSWindowActorChild> WindowGlobalChild::GetActor(
diff --git a/dom/ipc/WindowGlobalChild.h b/dom/ipc/WindowGlobalChild.h
index 3711cbeec27b..126583585f7b 100644
--- a/dom/ipc/WindowGlobalChild.h
+++ b/dom/ipc/WindowGlobalChild.h
@@ -111,7 +111,7 @@ class WindowGlobalChild final : public WindowGlobalActor,
                        JS::Handle<JSObject*> aGivenProto) override;
 
  protected:
-  const nsACString& GetRemoteType() override;
+  const nsAString& GetRemoteType() override;
 
   already_AddRefed<JSActor> InitJSActor(JS::HandleObject aMaybeActor,
                                         const nsACString& aName,
diff --git a/dom/ipc/WindowGlobalParent.cpp b/dom/ipc/WindowGlobalParent.cpp
index 84eee3060d5f..1f82a796673f 100644
--- a/dom/ipc/WindowGlobalParent.cpp
+++ b/dom/ipc/WindowGlobalParent.cpp
@@ -425,12 +425,12 @@ IPCResult WindowGlobalParent::RecvRawMessage(const JSActorMessageMeta& aMeta,
   return IPC_OK();
 }
 
-const nsACString& WindowGlobalParent::GetRemoteType() {
+const nsAString& WindowGlobalParent::GetRemoteType() {
   if (RefPtr<BrowserParent> browserParent = GetBrowserParent()) {
     return browserParent->Manager()->GetRemoteType();
   }
 
-  return NOT_REMOTE_TYPE;
+  return VoidString();
 }
 
 void WindowGlobalParent::NotifyContentBlockingEvent(
diff --git a/dom/ipc/WindowGlobalParent.h b/dom/ipc/WindowGlobalParent.h
index 61a3a5487c3b..3eabd962e175 100644
--- a/dom/ipc/WindowGlobalParent.h
+++ b/dom/ipc/WindowGlobalParent.h
@@ -194,7 +194,7 @@ class WindowGlobalParent final : public WindowContext,
 
   nsITransportSecurityInfo* GetSecurityInfo() { return mSecurityInfo; }
 
-  const nsACString& GetRemoteType() override;
+  const nsAString& GetRemoteType() override;
 
  protected:
   already_AddRefed<JSActor> InitJSActor(JS::HandleObject aMaybeActor,
diff --git a/dom/ipc/fuzztest/content_parent_ipc_libfuzz.cpp b/dom/ipc/fuzztest/content_parent_ipc_libfuzz.cpp
index a5067057023b..ef26fea6c6fc 100644
--- a/dom/ipc/fuzztest/content_parent_ipc_libfuzz.cpp
+++ b/dom/ipc/fuzztest/content_parent_ipc_libfuzz.cpp
@@ -19,7 +19,7 @@ int FuzzingInitContentParentIPC(int* argc, char*** argv) { return 0; }
 static int RunContentParentIPCFuzzing(const uint8_t* data, size_t size) {
   static mozilla::dom::ContentParent* p =
       mozilla::ipc::ProtocolFuzzerHelper::CreateContentParent(
-          DEFAULT_REMOTE_TYPE);
+          NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE));
 
   static nsTArray<nsCString> ignored = mozilla::ipc::LoadIPCMessageBlacklist(
       getenv("MOZ_IPC_MESSAGE_FUZZ_BLACKLIST"));
diff --git a/dom/ipc/jsactor/JSProcessActorProtocol.cpp b/dom/ipc/jsactor/JSProcessActorProtocol.cpp
index 7568d76957e3..eb796740657f 100644
--- a/dom/ipc/jsactor/JSProcessActorProtocol.cpp
+++ b/dom/ipc/jsactor/JSProcessActorProtocol.cpp
@@ -121,7 +121,7 @@ void JSProcessActorProtocol::RemoveObservers() {
 }
 
 bool JSProcessActorProtocol::RemoteTypePrefixMatches(
-    const nsDependentCSubstring& aRemoteType) {
+    const nsDependentSubstring& aRemoteType) {
   for (auto& remoteType : mRemoteTypes) {
     if (StringBeginsWith(aRemoteType, remoteType)) {
       return true;
@@ -130,7 +130,7 @@ bool JSProcessActorProtocol::RemoteTypePrefixMatches(
   return false;
 }
 
-bool JSProcessActorProtocol::Matches(const nsACString& aRemoteType) {
+bool JSProcessActorProtocol::Matches(const nsAString& aRemoteType) {
   if (!mRemoteTypes.IsEmpty() &&
       !RemoteTypePrefixMatches(RemoteTypePrefix(aRemoteType))) {
     return false;
diff --git a/dom/ipc/jsactor/JSProcessActorProtocol.h b/dom/ipc/jsactor/JSProcessActorProtocol.h
index b6440a493d2a..f54d6e8fd5cb 100644
--- a/dom/ipc/jsactor/JSProcessActorProtocol.h
+++ b/dom/ipc/jsactor/JSProcessActorProtocol.h
@@ -54,15 +54,15 @@ class JSProcessActorProtocol final : public JSActorProtocol,
 
   void AddObservers();
   void RemoveObservers();
-  bool Matches(const nsACString& aRemoteType);
+  bool Matches(const nsAString& aRemoteType);
 
  private:
   explicit JSProcessActorProtocol(const nsACString& aName) : mName(aName) {}
-  bool RemoteTypePrefixMatches(const nsDependentCSubstring& aRemoteType);
+  bool RemoteTypePrefixMatches(const nsDependentSubstring& aRemoteType);
   ~JSProcessActorProtocol() = default;
 
   nsCString mName;
-  nsTArray<nsCString> mRemoteTypes;
+  nsTArray<nsString> mRemoteTypes;
 
   ParentSide mParent;
   ChildSide mChild;
diff --git a/dom/ipc/jsactor/JSWindowActorProtocol.cpp b/dom/ipc/jsactor/JSWindowActorProtocol.cpp
index 1d15439117dd..8e78aa8e49a9 100644
--- a/dom/ipc/jsactor/JSWindowActorProtocol.cpp
+++ b/dom/ipc/jsactor/JSWindowActorProtocol.cpp
@@ -295,7 +295,7 @@ extensions::MatchPatternSet* JSWindowActorProtocol::GetURIMatcher() {
 }
 
 bool JSWindowActorProtocol::RemoteTypePrefixMatches(
-    const nsDependentCSubstring& aRemoteType) {
+    const nsDependentSubstring& aRemoteType) {
   for (auto& remoteType : mRemoteTypes) {
     if (StringBeginsWith(aRemoteType, remoteType)) {
       return true;
@@ -317,7 +317,7 @@ bool JSWindowActorProtocol::MessageManagerGroupMatches(
 
 bool JSWindowActorProtocol::Matches(BrowsingContext* aBrowsingContext,
                                     nsIURI* aURI,
-                                    const nsACString& aRemoteType) {
+                                    const nsAString& aRemoteType) {
   MOZ_ASSERT(aBrowsingContext, "DocShell without a BrowsingContext!");
   MOZ_ASSERT(aURI, "Must have URI!");
 
diff --git a/dom/ipc/jsactor/JSWindowActorProtocol.h b/dom/ipc/jsactor/JSWindowActorProtocol.h
index 452d4d588bc9..014766f4562c 100644
--- a/dom/ipc/jsactor/JSWindowActorProtocol.h
+++ b/dom/ipc/jsactor/JSWindowActorProtocol.h
@@ -70,12 +70,12 @@ class JSWindowActorProtocol final : public JSActorProtocol,
   void AddObservers();
   void RemoveObservers();
   bool Matches(BrowsingContext* aBrowsingContext, nsIURI* aURI,
-               const nsACString& aRemoteType);
+               const nsAString& aRemoteType);
 
  private:
   explicit JSWindowActorProtocol(const nsACString& aName) : mName(aName) {}
   extensions::MatchPatternSet* GetURIMatcher();
-  bool RemoteTypePrefixMatches(const nsDependentCSubstring& aRemoteType);
+  bool RemoteTypePrefixMatches(const nsDependentSubstring& aRemoteType);
   bool MessageManagerGroupMatches(BrowsingContext* aBrowsingContext);
   ~JSWindowActorProtocol() = default;
 
@@ -83,7 +83,7 @@ class JSWindowActorProtocol final : public JSActorProtocol,
   bool mAllFrames = false;
   bool mIncludeChrome = false;
   nsTArray<nsString> mMatches;
-  nsTArray<nsCString> mRemoteTypes;
+  nsTArray<nsString> mRemoteTypes;
   nsTArray<nsString> mMessageManagerGroups;
 
   ParentSide mParent;
diff --git a/dom/ipc/moz.build b/dom/ipc/moz.build
index 461c3cb9c97d..27ff1695cd06 100644
--- a/dom/ipc/moz.build
+++ b/dom/ipc/moz.build
@@ -60,7 +60,6 @@ EXPORTS.mozilla.dom += [
     'ReferrerInfoUtils.h',
     'RefMessageBodyService.h',
     'RemoteBrowser.h',
-    'RemoteType.h',
     'RemoteWebProgress.h',
     'RemoteWebProgressRequest.h',
     'SharedMessageBody.h',
diff --git a/dom/push/PushNotifier.cpp b/dom/push/PushNotifier.cpp
index d8806d081c55..59940ff53c74 100644
--- a/dom/push/PushNotifier.cpp
+++ b/dom/push/PushNotifier.cpp
@@ -103,7 +103,8 @@ nsresult PushNotifier::Dispatch(PushDispatcher& aDispatcher) {
         // remote type is acceptable. This should not run when Fission is
         // enabled, and we specifically don't want this for
         // LARGE_ALLOCATION_REMOTE_TYPE, so don't use IsWebRemoteType().
-        if (contentActors[i]->GetRemoteType() != DEFAULT_REMOTE_TYPE) {
+        if (!contentActors[i]->GetRemoteType().EqualsLiteral(
+                DEFAULT_REMOTE_TYPE)) {
           continue;
         }
 
diff --git a/dom/webidl/MozFrameLoaderOwner.webidl b/dom/webidl/MozFrameLoaderOwner.webidl
index 865f436fd066..320cf6010f5c 100644
--- a/dom/webidl/MozFrameLoaderOwner.webidl
+++ b/dom/webidl/MozFrameLoaderOwner.webidl
@@ -5,7 +5,7 @@
  */
 
 dictionary RemotenessOptions {
-  required UTF8String? remoteType;
+  required DOMString? remoteType;
 
   // Used to resume a given channel load within the target process. If present,
   // it will be used rather than the `src` & `srcdoc` attributes on the
diff --git a/dom/workers/remoteworkers/RemoteWorkerManager.cpp b/dom/workers/remoteworkers/RemoteWorkerManager.cpp
index 0f64f09879a8..72de3791ceb1 100644
--- a/dom/workers/remoteworkers/RemoteWorkerManager.cpp
+++ b/dom/workers/remoteworkers/RemoteWorkerManager.cpp
@@ -60,8 +60,8 @@ void TransmitPermissionsAndBlobURLsForPrincipalInfo(
 }  // namespace
 
 // static
-bool RemoteWorkerManager::MatchRemoteType(const nsACString& processRemoteType,
-                                          const nsACString& workerRemoteType) {
+bool RemoteWorkerManager::MatchRemoteType(const nsAString& processRemoteType,
+                                          const nsAString& workerRemoteType) {
   if (processRemoteType.Equals(workerRemoteType)) {
     return true;
   }
@@ -89,7 +89,7 @@ bool RemoteWorkerManager::MatchRemoteType(const nsACString& processRemoteType,
 }
 
 // static
-Result<nsCString, nsresult> RemoteWorkerManager::GetRemoteType(
+Result<nsString, nsresult> RemoteWorkerManager::GetRemoteType(
     const nsCOMPtr<nsIPrincipal>& aPrincipal, WorkerType aWorkerType) {
   AssertIsOnMainThread();
 
@@ -100,7 +100,7 @@ Result<nsCString, nsresult> RemoteWorkerManager::GetRemoteType(
     return Err(NS_ERROR_UNEXPECTED);
   }
 
-  nsCString remoteType = NOT_REMOTE_TYPE;
+  nsString remoteType;
 
   // If Gecko is running in single process mode, there is no child process
   // to select, return without assigning any remoteType.
@@ -131,21 +131,23 @@ Result<nsCString, nsresult> RemoteWorkerManager::GetRemoteType(
       "browser.tabs.remote.separatePrivilegedMozillaWebContentProcess", false);
 
   if (isMozExtension) {
-    remoteType = EXTENSION_REMOTE_TYPE;
+    remoteType.Assign(NS_LITERAL_STRING_FROM_CSTRING(EXTENSION_REMOTE_TYPE));
   } else if (separatePrivilegedMozilla) {
     bool isPrivilegedMozilla = false;
     aPrincipal->IsURIInPrefList("browser.tabs.remote.separatedMozillaDomains",
                                 &isPrivilegedMozilla);
 
     if (isPrivilegedMozilla) {
-      remoteType = PRIVILEGEDMOZILLA_REMOTE_TYPE;
-    } else if (aWorkerType == WorkerType::WorkerTypeShared && contentChild) {
-      remoteType = contentChild->GetRemoteType();
+      remoteType.Assign(
+          NS_LITERAL_STRING_FROM_CSTRING(PRIVILEGEDMOZILLA_REMOTE_TYPE));
     } else {
-      remoteType = DEFAULT_REMOTE_TYPE;
+      remoteType.Assign(
+          aWorkerType == WorkerType::WorkerTypeShared && contentChild
+              ? contentChild->GetRemoteType()
+              : NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE));
     }
   } else {
-    remoteType = DEFAULT_REMOTE_TYPE;
+    remoteType.Assign(NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE));
   }
 
   return remoteType;
@@ -347,7 +349,7 @@ void RemoteWorkerManager::AsyncCreationFailed(
 }
 
 /* static */
-nsCString RemoteWorkerManager::GetRemoteTypeForActor(
+nsString RemoteWorkerManager::GetRemoteTypeForActor(
     const RemoteWorkerServiceParent* aActor) {
   AssertIsInMainProcess();
   AssertIsOnBackgroundThread();
@@ -360,10 +362,10 @@ nsCString RemoteWorkerManager::GetRemoteTypeForActor(
       MakeScopeExit([&] { NS_ReleaseOnMainThread(contentParent.forget()); });
 
   if (NS_WARN_IF(!contentParent)) {
-    return EmptyCString();
+    return EmptyString();
   }
 
-  nsCString aRemoteType(contentParent->GetRemoteType());
+  nsString aRemoteType(contentParent->GetRemoteType());
 
   return aRemoteType;
 }
@@ -549,7 +551,7 @@ void RemoteWorkerManager::LaunchNewContentProcess(
                                 bgEventTarget = std::move(bgEventTarget),
                                 self = RefPtr<RemoteWorkerManager>(this)](
                                    const CallbackParamType& aValue,
-                                   const nsCString& remoteType) mutable {
+                                   const nsString& remoteType) mutable {
     if (aValue.IsResolve()) {
       if (isServiceWorker) {
         TransmitPermissionsAndBlobURLsForPrincipalInfo(aValue.ResolveValue(),
@@ -586,7 +588,9 @@ void RemoteWorkerManager::LaunchNewContentProcess(
       __func__, [callback = std::move(processLaunchCallback),
                  workerRemoteType = aData.remoteType()]() mutable {
         auto remoteType =
-            workerRemoteType.IsEmpty() ? DEFAULT_REMOTE_TYPE : workerRemoteType;
+            workerRemoteType.IsEmpty()
+                ? NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE)
+                : workerRemoteType;
 
         ContentParent::GetNewOrUsedBrowserProcessAsync(
             /* aFrameElement = */ nullptr,
diff --git a/dom/workers/remoteworkers/RemoteWorkerManager.h b/dom/workers/remoteworkers/RemoteWorkerManager.h
index 86f97534ab2a..ecf5218498cc 100644
--- a/dom/workers/remoteworkers/RemoteWorkerManager.h
+++ b/dom/workers/remoteworkers/RemoteWorkerManager.h
@@ -35,14 +35,14 @@ class RemoteWorkerManager final {
   void Launch(RemoteWorkerController* aController,
               const RemoteWorkerData& aData, base::ProcessId aProcessId);
 
-  static bool MatchRemoteType(const nsACString& processRemoteType,
-                              const nsACString& workerRemoteType);
+  static bool MatchRemoteType(const nsAString& processRemoteType,
+                              const nsAString& workerRemoteType);
 
   /**
    * Get the child process RemoteType where a RemoteWorker should be
    * launched.
    */
-  static Result<nsCString, nsresult> GetRemoteType(
+  static Result<nsString, nsresult> GetRemoteType(
       const nsCOMPtr<nsIPrincipal>& aPrincipal, WorkerType aWorkerType);
 
   /**
@@ -73,7 +73,7 @@ class RemoteWorkerManager final {
 
   void AsyncCreationFailed(RemoteWorkerController* aController);
 
-  static nsCString GetRemoteTypeForActor(
+  static nsString GetRemoteTypeForActor(
       const RemoteWorkerServiceParent* aActor);
 
   // Iterate through all RemoteWorkerServiceParent actors, starting from a
diff --git a/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh b/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh
index a282d6ee7f03..c9018fbc04bc 100644
--- a/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh
+++ b/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh
@@ -72,7 +72,7 @@ struct RemoteWorkerData
   nsID agentClusterId;
 
   // Child process remote type where the worker should only run on.
-  nsCString remoteType;
+  nsString remoteType;
 };
 
 // ErrorData/ErrorDataNote correspond to WorkerErrorReport/WorkerErrorNote
diff --git a/dom/workers/remoteworkers/gtest/TestMatchRemoteType.cpp b/dom/workers/remoteworkers/gtest/TestMatchRemoteType.cpp
index 10016a52c2d7..916a77d44eab 100644
--- a/dom/workers/remoteworkers/gtest/TestMatchRemoteType.cpp
+++ b/dom/workers/remoteworkers/gtest/TestMatchRemoteType.cpp
@@ -12,39 +12,54 @@ using namespace mozilla::dom;
 TEST(RemoteWorkerManager, TestMatchRemoteType)
 {
   static const struct {
-    const nsCString processRemoteType;
-    const nsCString workerRemoteType;
+    const nsString processRemoteType;
+    const nsString workerRemoteType;
     const bool shouldMatch;
   } tests[] = {
       // Test exact matches between process and worker remote types.
-      {DEFAULT_REMOTE_TYPE, DEFAULT_REMOTE_TYPE, true},
-      {EXTENSION_REMOTE_TYPE, EXTENSION_REMOTE_TYPE, true},
-      {PRIVILEGEDMOZILLA_REMOTE_TYPE, PRIVILEGEDMOZILLA_REMOTE_TYPE, true},
+      {NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE),
+       NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE), true},
+      {NS_LITERAL_STRING_FROM_CSTRING(EXTENSION_REMOTE_TYPE),
+       NS_LITERAL_STRING_FROM_CSTRING(EXTENSION_REMOTE_TYPE), true},
+      {NS_LITERAL_STRING_FROM_CSTRING(PRIVILEGEDMOZILLA_REMOTE_TYPE),
+       NS_LITERAL_STRING_FROM_CSTRING(PRIVILEGEDMOZILLA_REMOTE_TYPE), true},
 
       // Test workers with remoteType "web" not launched on non-web or coop+coep
       // processes.
-      {PRIVILEGEDMOZILLA_REMOTE_TYPE, DEFAULT_REMOTE_TYPE, false},
-      {PRIVILEGEDABOUT_REMOTE_TYPE, DEFAULT_REMOTE_TYPE, false},
-      {EXTENSION_REMOTE_TYPE, DEFAULT_REMOTE_TYPE, false},
-      {FILE_REMOTE_TYPE, DEFAULT_REMOTE_TYPE, false},
-      {WITH_COOP_COEP_REMOTE_TYPE_PREFIX, DEFAULT_REMOTE_TYPE, false},
+      {NS_LITERAL_STRING_FROM_CSTRING(PRIVILEGEDMOZILLA_REMOTE_TYPE),
+       NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE), false},
+      {NS_LITERAL_STRING_FROM_CSTRING(PRIVILEGEDABOUT_REMOTE_TYPE),
+       NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE), false},
+      {NS_LITERAL_STRING_FROM_CSTRING(EXTENSION_REMOTE_TYPE),
+       NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE), false},
+      {NS_LITERAL_STRING_FROM_CSTRING(FILE_REMOTE_TYPE),
+       NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE), false},
+      {NS_LITERAL_STRING_FROM_CSTRING(WITH_COOP_COEP_REMOTE_TYPE_PREFIX),
+       NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE), false},
 
       // Test workers with remoteType "web" launched in web child processes.
-      {LARGE_ALLOCATION_REMOTE_TYPE, DEFAULT_REMOTE_TYPE, true},
-      {FISSION_WEB_REMOTE_TYPE, DEFAULT_REMOTE_TYPE, true},
+      {NS_LITERAL_STRING_FROM_CSTRING(LARGE_ALLOCATION_REMOTE_TYPE),
+       NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE), true},
+      {NS_LITERAL_STRING_FROM_CSTRING(FISSION_WEB_REMOTE_TYPE),
+       NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE), true},
 
       // Test empty remoteType default to "web" remoteType.
-      {DEFAULT_REMOTE_TYPE, NOT_REMOTE_TYPE, true},
-      {WITH_COOP_COEP_REMOTE_TYPE_PREFIX, NOT_REMOTE_TYPE, false},
-      {PRIVILEGEDMOZILLA_REMOTE_TYPE, NOT_REMOTE_TYPE, false},
-      {EXTENSION_REMOTE_TYPE, NOT_REMOTE_TYPE, false},
+      {NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE), EmptyString(),
+       true},
+      {NS_LITERAL_STRING_FROM_CSTRING(WITH_COOP_COEP_REMOTE_TYPE_PREFIX),
+       EmptyString(), false},
+      {NS_LITERAL_STRING_FROM_CSTRING(PRIVILEGEDMOZILLA_REMOTE_TYPE),
+       EmptyString(), false},
+      {NS_LITERAL_STRING_FROM_CSTRING(EXTENSION_REMOTE_TYPE), EmptyString(),
+       false},
   };
 
   for (const auto& test : tests) {
-    auto message = nsPrintfCString(
-        R"(MatchRemoteType("%s", "%s") should return %s)",
-        test.processRemoteType.get(), test.workerRemoteType.get(),
-        test.shouldMatch ? "true" : "false");
+    auto message =
+        nsPrintfCString(R"(MatchRemoteType("%s", "%s") should return %s)",
+                        NS_ConvertUTF16toUTF8(test.processRemoteType).get(),
+                        NS_ConvertUTF16toUTF8(test.workerRemoteType).get(),
+                        test.shouldMatch ? "true" : "false");
     ASSERT_EQ(RemoteWorkerManager::MatchRemoteType(test.processRemoteType,
                                                    test.workerRemoteType),
               test.shouldMatch)
diff --git a/ipc/glue/BackgroundParentImpl.cpp b/ipc/glue/BackgroundParentImpl.cpp
index 62679ad3500a..6412a4db7937 100644
--- a/ipc/glue/BackgroundParentImpl.cpp
+++ b/ipc/glue/BackgroundParentImpl.cpp
@@ -579,7 +579,7 @@ mozilla::ipc::IPCResult BackgroundParentImpl::RecvPFileCreatorConstructor(
   if (!parent) {
     isFileRemoteType = true;
   } else {
-    isFileRemoteType = parent->GetRemoteType() == FILE_REMOTE_TYPE;
+    isFileRemoteType = parent->GetRemoteType().EqualsLiteral(FILE_REMOTE_TYPE);
     NS_ReleaseOnMainThread("ContentParent release", parent.forget());
   }
 
diff --git a/js/xpconnect/loader/ScriptPreloader.cpp b/js/xpconnect/loader/ScriptPreloader.cpp
index 7e8e6844cf18..10b30331ebc8 100644
--- a/js/xpconnect/loader/ScriptPreloader.cpp
+++ b/js/xpconnect/loader/ScriptPreloader.cpp
@@ -185,11 +185,11 @@ void ScriptPreloader::InitContentChild(ContentParent& parent) {
   }
 }
 
-ProcessType ScriptPreloader::GetChildProcessType(const nsACString& remoteType) {
-  if (remoteType == EXTENSION_REMOTE_TYPE) {
+ProcessType ScriptPreloader::GetChildProcessType(const nsAString& remoteType) {
+  if (remoteType.EqualsLiteral(EXTENSION_REMOTE_TYPE)) {
     return ProcessType::Extension;
   }
-  if (remoteType == PRIVILEGEDABOUT_REMOTE_TYPE) {
+  if (remoteType.EqualsLiteral(PRIVILEGEDABOUT_REMOTE_TYPE)) {
     return ProcessType::PrivilegedAbout;
   }
   return ProcessType::Web;
diff --git a/js/xpconnect/loader/ScriptPreloader.h b/js/xpconnect/loader/ScriptPreloader.h
index d0df0571658c..a26388dcffe4 100644
--- a/js/xpconnect/loader/ScriptPreloader.h
+++ b/js/xpconnect/loader/ScriptPreloader.h
@@ -75,7 +75,7 @@ class ScriptPreloader : public nsIObserver,
   static ScriptPreloader& GetSingleton();
   static ScriptPreloader& GetChildSingleton();
 
-  static ProcessType GetChildProcessType(const nsACString& remoteType);
+  static ProcessType GetChildProcessType(const nsAString& remoteType);
 
   // Retrieves the script with the given cache key from the script cache.
   // Returns null if the script is not cached.
diff --git a/netwerk/base/SimpleChannelParent.cpp b/netwerk/base/SimpleChannelParent.cpp
index 01029d74ebde..c8617c2a7357 100644
--- a/netwerk/base/SimpleChannelParent.cpp
+++ b/netwerk/base/SimpleChannelParent.cpp
@@ -64,7 +64,7 @@ SimpleChannelParent::Delete() {
 }
 
 NS_IMETHODIMP
-SimpleChannelParent::GetRemoteType(nsACString& aRemoteType) {
+SimpleChannelParent::GetRemoteType(nsAString& aRemoteType) {
   return NS_ERROR_NOT_IMPLEMENTED;
 }
 
diff --git a/netwerk/base/nsIParentChannel.idl b/netwerk/base/nsIParentChannel.idl
index 137d1907bdfb..6d6f487865d4 100644
--- a/netwerk/base/nsIParentChannel.idl
+++ b/netwerk/base/nsIParentChannel.idl
@@ -77,5 +77,5 @@ interface nsIParentChannel : nsIStreamListener
   /**
    * The remote type of the target process for this load.
    */
-  readonly attribute AUTF8String remoteType;
+  readonly attribute AString remoteType;
 };
diff --git a/netwerk/ipc/DocumentLoadListener.cpp b/netwerk/ipc/DocumentLoadListener.cpp
index b09c4ddde64d..fbb5dc9f3198 100644
--- a/netwerk/ipc/DocumentLoadListener.cpp
+++ b/netwerk/ipc/DocumentLoadListener.cpp
@@ -1314,7 +1314,7 @@ bool DocumentLoadListener::MaybeTriggerProcessSwitch(
     return false;
   }
 
-  nsAutoCString currentRemoteType(NOT_REMOTE_TYPE);
+  nsAutoString currentRemoteType(VoidString());
   if (RefPtr<ContentParent> contentParent =
           browsingContext->GetContentParent()) {
     currentRemoteType = contentParent->GetRemoteType();
@@ -1322,7 +1322,7 @@ bool DocumentLoadListener::MaybeTriggerProcessSwitch(
   MOZ_ASSERT_IF(currentRemoteType.IsEmpty(), !OtherPid());
 
   // Determine what type of content process this load should finish in.
-  nsAutoCString preferredRemoteType(currentRemoteType);
+  nsAutoString preferredRemoteType(currentRemoteType);
   bool replaceBrowsingContext = false;
   uint64_t specificGroupId = 0;
 
@@ -1370,12 +1370,13 @@ bool DocumentLoadListener::MaybeTriggerProcessSwitch(
       // high-resolution timers.
       nsAutoCString siteOrigin;
       resultPrincipal->GetSiteOrigin(siteOrigin);
-      preferredRemoteType = WITH_COOP_COEP_REMOTE_TYPE_PREFIX;
-      preferredRemoteType.Append(siteOrigin);
+      preferredRemoteType =
+          NS_LITERAL_STRING_FROM_CSTRING(WITH_COOP_COEP_REMOTE_TYPE_PREFIX);
+      AppendUTF8toUTF16(siteOrigin, preferredRemoteType);
     } else if (isCOOPSwitch) {
       // If we're doing a COOP switch, we do not need any affinity to the
       // current remote type. Clear it back to the default value.
-      preferredRemoteType = DEFAULT_REMOTE_TYPE;
+      preferredRemoteType = NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE);
     }
   }
 
@@ -1386,10 +1387,12 @@ bool DocumentLoadListener::MaybeTriggerProcessSwitch(
   if (browsingContext->IsTop() &&
       browsingContext->Group()->Toplevels().Length() == 1) {
     if (IsLargeAllocationLoad(browsingContext, mChannel)) {
-      preferredRemoteType = LARGE_ALLOCATION_REMOTE_TYPE;
+      preferredRemoteType =
+          NS_LITERAL_STRING_FROM_CSTRING(LARGE_ALLOCATION_REMOTE_TYPE);
       replaceBrowsingContext = true;
-    } else if (preferredRemoteType == LARGE_ALLOCATION_REMOTE_TYPE) {
-      preferredRemoteType = DEFAULT_REMOTE_TYPE;
+    } else if (preferredRemoteType.EqualsLiteral(
+                   LARGE_ALLOCATION_REMOTE_TYPE)) {
+      preferredRemoteType = NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE);
       replaceBrowsingContext = true;
     }
   }
@@ -1401,9 +1404,10 @@ bool DocumentLoadListener::MaybeTriggerProcessSwitch(
       // Toplevel extension BrowsingContexts must be loaded in the extension
       // browsing context group, within the extension content process.
       if (ExtensionPolicyService::GetSingleton().UseRemoteExtensions()) {
-        preferredRemoteType = EXTENSION_REMOTE_TYPE;
+        preferredRemoteType =
+            NS_LITERAL_STRING_FROM_CSTRING(EXTENSION_REMOTE_TYPE);
       } else {
-        preferredRemoteType = NOT_REMOTE_TYPE;
+        preferredRemoteType = VoidString();
       }
 
       if (browsingContext->Group()->Id() !=
@@ -1422,7 +1426,8 @@ bool DocumentLoadListener::MaybeTriggerProcessSwitch(
   LOG(
       ("DocumentLoadListener GetRemoteTypeForPrincipal "
        "[this=%p, contentParent=%s, preferredRemoteType=%s]",
-       this, currentRemoteType.get(), preferredRemoteType.get()));
+       this, NS_ConvertUTF16toUTF8(currentRemoteType).get(),
+       NS_ConvertUTF16toUTF8(preferredRemoteType).get()));
 
   nsCOMPtr<nsIE10SUtils> e10sUtils =
       do_ImportModule("resource://gre/modules/E10SUtils.jsm", "E10SUtils");
@@ -1437,7 +1442,7 @@ bool DocumentLoadListener::MaybeTriggerProcessSwitch(
     currentPrincipal = wgp->DocumentPrincipal();
   }
 
-  nsAutoCString remoteType;
+  nsAutoString remoteType;
   rv = e10sUtils->GetRemoteTypeForPrincipal(
       resultPrincipal, mChannelCreationURI, browsingContext->UseRemoteTabs(),
       browsingContext->UseRemoteSubframes(), preferredRemoteType,
@@ -1451,16 +1456,18 @@ bool DocumentLoadListener::MaybeTriggerProcessSwitch(
   // other remote type, ensure the browsing context is replaced so that we leave
   // the extension-specific BrowsingContextGroup.
   if (browsingContext->IsTop() && currentRemoteType != remoteType &&
-      currentRemoteType == EXTENSION_REMOTE_TYPE) {
+      currentRemoteType.EqualsLiteral(EXTENSION_REMOTE_TYPE)) {
     replaceBrowsingContext = true;
   }
 
   LOG(("GetRemoteTypeForPrincipal -> current:%s remoteType:%s",
-       currentRemoteType.get(), remoteType.get()));
+       NS_ConvertUTF16toUTF8(currentRemoteType).get(),
+       NS_ConvertUTF16toUTF8(remoteType).get()));
 
   // Check if a process switch is needed.
   if (currentRemoteType == remoteType && !replaceBrowsingContext) {
-    LOG(("Process Switch Abort: type (%s) is compatible", remoteType.get()));
+    LOG(("Process Switch Abort: type (%s) is compatible",
+         NS_ConvertUTF16toUTF8(remoteType).get()));
     return false;
   }
 
@@ -1472,7 +1479,8 @@ bool DocumentLoadListener::MaybeTriggerProcessSwitch(
   *aWillSwitchToRemote = !remoteType.IsEmpty();
 
   LOG(("Process Switch: Changing Remoteness from '%s' to '%s'",
-       currentRemoteType.get(), remoteType.get()));
+       NS_ConvertUTF16toUTF8(currentRemoteType).get(),
+       NS_ConvertUTF16toUTF8(remoteType).get()));
 
   mDoingProcessSwitch = true;
 
@@ -2030,7 +2038,7 @@ DocumentLoadListener::Delete() {
 }
 
 NS_IMETHODIMP
-DocumentLoadListener::GetRemoteType(nsACString& aRemoteType) {
+DocumentLoadListener::GetRemoteType(nsAString& aRemoteType) {
   RefPtr<CanonicalBrowsingContext> browsingContext = GetBrowsingContext();
   if (!browsingContext) {
     return NS_ERROR_UNEXPECTED;
@@ -2039,7 +2047,7 @@ DocumentLoadListener::GetRemoteType(nsACString& aRemoteType) {
   ErrorResult error;
   browsingContext->GetCurrentRemoteType(aRemoteType, error);
   if (error.Failed()) {
-    aRemoteType = NOT_REMOTE_TYPE;
+    aRemoteType = VoidString();
   }
   return NS_OK;
 }
diff --git a/netwerk/ipc/NeckoParent.cpp b/netwerk/ipc/NeckoParent.cpp
index 6dcd332d21c1..eaebfa069097 100644
--- a/netwerk/ipc/NeckoParent.cpp
+++ b/netwerk/ipc/NeckoParent.cpp
@@ -899,8 +899,8 @@ mozilla::ipc::IPCResult NeckoParent::RecvGetPageThumbStream(
   // ScriptSecurityManager, but if somehow the process has been tricked into
   // sending this message, we send IPC_FAIL in order to crash that
   // likely-compromised content process.
-  if (static_cast<ContentParent*>(Manager())->GetRemoteType() !=
-      PRIVILEGEDABOUT_REMOTE_TYPE) {
+  if (!static_cast<ContentParent*>(Manager())->GetRemoteType().EqualsLiteral(
+          PRIVILEGEDABOUT_REMOTE_TYPE)) {
     return IPC_FAIL(this, "Wrong process type");
   }
 
diff --git a/netwerk/ipc/ParentChannelWrapper.cpp b/netwerk/ipc/ParentChannelWrapper.cpp
index c2c5eb858094..953cf4b1fcfd 100644
--- a/netwerk/ipc/ParentChannelWrapper.cpp
+++ b/netwerk/ipc/ParentChannelWrapper.cpp
@@ -87,8 +87,8 @@ NS_IMETHODIMP
 ParentChannelWrapper::Delete() { return NS_OK; }
 
 NS_IMETHODIMP
-ParentChannelWrapper::GetRemoteType(nsACString& aRemoteType) {
-  aRemoteType = NOT_REMOTE_TYPE;
+ParentChannelWrapper::GetRemoteType(nsAString& aRemoteType) {
+  aRemoteType = VoidString();
   return NS_OK;
 }
 
diff --git a/netwerk/protocol/data/DataChannelParent.cpp b/netwerk/protocol/data/DataChannelParent.cpp
index 025cc2060e76..2c501faa3cee 100644
--- a/netwerk/protocol/data/DataChannelParent.cpp
+++ b/netwerk/protocol/data/DataChannelParent.cpp
@@ -66,7 +66,7 @@ DataChannelParent::Delete() {
 }
 
 NS_IMETHODIMP
-DataChannelParent::GetRemoteType(nsACString& aRemoteType) {
+DataChannelParent::GetRemoteType(nsAString& aRemoteType) {
   if (!CanSend()) {
     return NS_ERROR_UNEXPECTED;
   }
diff --git a/netwerk/protocol/file/FileChannelParent.cpp b/netwerk/protocol/file/FileChannelParent.cpp
index 904b9fa88f4b..3c8f01062dfb 100644
--- a/netwerk/protocol/file/FileChannelParent.cpp
+++ b/netwerk/protocol/file/FileChannelParent.cpp
@@ -66,7 +66,7 @@ FileChannelParent::Delete() {
 }
 
 NS_IMETHODIMP
-FileChannelParent::GetRemoteType(nsACString& aRemoteType) {
+FileChannelParent::GetRemoteType(nsAString& aRemoteType) {
   if (!CanSend()) {
     return NS_ERROR_UNEXPECTED;
   }
diff --git a/netwerk/protocol/ftp/FTPChannelParent.cpp b/netwerk/protocol/ftp/FTPChannelParent.cpp
index 330616020a55..0515344a3d36 100644
--- a/netwerk/protocol/ftp/FTPChannelParent.cpp
+++ b/netwerk/protocol/ftp/FTPChannelParent.cpp
@@ -533,7 +533,7 @@ FTPChannelParent::Delete() {
 }
 
 NS_IMETHODIMP
-FTPChannelParent::GetRemoteType(nsACString& aRemoteType) {
+FTPChannelParent::GetRemoteType(nsAString& aRemoteType) {
   if (!CanSend()) {
     return NS_ERROR_UNEXPECTED;
   }
diff --git a/netwerk/protocol/http/HttpChannelParent.cpp b/netwerk/protocol/http/HttpChannelParent.cpp
index 8a1c022406e9..e5c4b792026f 100644
--- a/netwerk/protocol/http/HttpChannelParent.cpp
+++ b/netwerk/protocol/http/HttpChannelParent.cpp
@@ -1997,7 +1997,7 @@ HttpChannelParent::Delete() {
 }
 
 NS_IMETHODIMP
-HttpChannelParent::GetRemoteType(nsACString& aRemoteType) {
+HttpChannelParent::GetRemoteType(nsAString& aRemoteType) {
   if (!CanSend()) {
     return NS_ERROR_UNEXPECTED;
   }
diff --git a/security/sandbox/linux/glue/SandboxPrefBridge.cpp b/security/sandbox/linux/glue/SandboxPrefBridge.cpp
index 9782e58817df..53a9870a3a4e 100644
--- a/security/sandbox/linux/glue/SandboxPrefBridge.cpp
+++ b/security/sandbox/linux/glue/SandboxPrefBridge.cpp
@@ -30,7 +30,7 @@ ContentProcessSandboxParams::ForThisProcess(
   // (Otherwise, mBrokerFd will remain -1 from the default ctor.)
 
   auto* cc = dom::ContentChild::GetSingleton();
-  params.mFileProcess = cc->GetRemoteType() == FILE_REMOTE_TYPE;
+  params.mFileProcess = cc->GetRemoteType().EqualsLiteral(FILE_REMOTE_TYPE);
 
   nsAutoCString extraSyscalls;
   nsresult rv = Preferences::GetCString(
diff --git a/toolkit/components/backgroundhangmonitor/BackgroundHangMonitor.cpp b/toolkit/components/backgroundhangmonitor/BackgroundHangMonitor.cpp
index 1bc5ad357da4..16c28de69830 100644
--- a/toolkit/components/backgroundhangmonitor/BackgroundHangMonitor.cpp
+++ b/toolkit/components/backgroundhangmonitor/BackgroundHangMonitor.cpp
@@ -22,7 +22,6 @@
 #include "mozilla/Telemetry.h"
 #include "mozilla/ThreadLocal.h"
 #include "mozilla/Unused.h"
-#include "mozilla/dom/RemoteType.h"
 #include "nsAppDirectoryServiceDefs.h"
 #include "nsIObserver.h"
 #include "nsIObserverService.h"
@@ -506,7 +505,7 @@ void BackgroundHangThread::ReportHang(TimeDuration aHangTime,
 
   HangDetails hangDetails(aHangTime,
                           nsDependentCString(XRE_GetProcessTypeString()),
-                          NOT_REMOTE_TYPE, mThreadName, mRunnableName,
+                          VoidString(), mThreadName, mRunnableName,
                           std::move(mHangStack), std::move(mAnnotations));
 
   PersistedToDisk persistedToDisk = aPersistedToDisk;
diff --git a/toolkit/components/backgroundhangmonitor/HangDetails.cpp b/toolkit/components/backgroundhangmonitor/HangDetails.cpp
index b940bb4b846f..250bcfc216ab 100644
--- a/toolkit/components/backgroundhangmonitor/HangDetails.cpp
+++ b/toolkit/components/backgroundhangmonitor/HangDetails.cpp
@@ -55,7 +55,7 @@ nsHangDetails::GetProcess(nsACString& aName) {
 }
 
 NS_IMETHODIMP
-nsHangDetails::GetRemoteType(nsACString& aName) {
+nsHangDetails::GetRemoteType(nsAString& aName) {
   aName.Assign(mDetails.remoteType());
   return NS_OK;
 }
@@ -574,7 +574,7 @@ Result<HangDetails, nsresult> ReadHangDetailsFromFile(nsIFile* aFile) {
   MOZ_TRY_VAR(result.threadName(), ReadTString<char>(fd));
   MOZ_TRY_VAR(result.runnableName(), ReadTString<char>(fd));
   MOZ_TRY_VAR(result.process(), ReadTString<char>(fd));
-  MOZ_TRY_VAR(result.remoteType(), ReadTString<char>(fd));
+  MOZ_TRY_VAR(result.remoteType(), ReadTString<char16_t>(fd));
 
   uint32_t numAnnotations;
   MOZ_TRY_VAR(numAnnotations, ReadUint(fd));
diff --git a/toolkit/components/backgroundhangmonitor/HangTypes.ipdlh b/toolkit/components/backgroundhangmonitor/HangTypes.ipdlh
index 3d8dd5aff2e1..44fd4d322fd7 100644
--- a/toolkit/components/backgroundhangmonitor/HangTypes.ipdlh
+++ b/toolkit/components/backgroundhangmonitor/HangTypes.ipdlh
@@ -85,7 +85,7 @@ struct HangDetails
 {
     TimeDuration duration;
     nsCString process;
-    nsCString remoteType;
+    nsString remoteType;
     nsCString threadName;
     nsCString runnableName;
     HangStack stack;
diff --git a/toolkit/components/backgroundhangmonitor/nsIHangDetails.idl b/toolkit/components/backgroundhangmonitor/nsIHangDetails.idl
index f9c6ba2de06b..7e15ebd5f020 100644
--- a/toolkit/components/backgroundhangmonitor/nsIHangDetails.idl
+++ b/toolkit/components/backgroundhangmonitor/nsIHangDetails.idl
@@ -50,7 +50,7 @@ interface nsIHangDetails : nsISupports
   /**
    * The remote type of the content process which produced the hang.
    */
-  readonly attribute AUTF8String remoteType;
+  readonly attribute AString remoteType;
 
   /**
    * Returns the stack which was captured by BHR. The offset is encoded as a hex
diff --git a/toolkit/components/extensions/ExtensionPolicyService.cpp b/toolkit/components/extensions/ExtensionPolicyService.cpp
index 8138694674da..3c63e3f8f920 100644
--- a/toolkit/components/extensions/ExtensionPolicyService.cpp
+++ b/toolkit/components/extensions/ExtensionPolicyService.cpp
@@ -119,7 +119,7 @@ bool ExtensionPolicyService::IsExtensionProcess() const {
 
   if (isRemote && XRE_IsContentProcess()) {
     auto& remoteType = dom::ContentChild::GetSingleton()->GetRemoteType();
-    return remoteType == EXTENSION_REMOTE_TYPE;
+    return remoteType.EqualsLiteral(EXTENSION_REMOTE_TYPE);
   }
   return !isRemote && XRE_IsParentProcess();
 }
diff --git a/toolkit/modules/nsIE10SUtils.idl b/toolkit/modules/nsIE10SUtils.idl
index 7419827b3837..d56939fbee7d 100644
--- a/toolkit/modules/nsIE10SUtils.idl
+++ b/toolkit/modules/nsIE10SUtils.idl
@@ -32,11 +32,11 @@ interface nsIE10SUtils : nsISupports {
    *
    * @return  The remote type to complete this load in.
    */
-  AUTF8String getRemoteTypeForPrincipal(in nsIPrincipal aPrincipal,
-                                        in nsIURI aChannelOriginalURI,
-                                        in boolean aMultiProcess,
-                                        in boolean aRemoteSubframes,
-                                        in AUTF8String aPreferredRemoteType,
-                                        in nsIPrincipal aCurrentPrincipal,
-                                        in boolean aIsSubframe);
+  AString getRemoteTypeForPrincipal(in nsIPrincipal aPrincipal,
+                                    in nsIURI aChannelOriginalURI,
+                                    in boolean aMultiProcess,
+                                    in boolean aRemoteSubframes,
+                                    in AString aPreferredRemoteType,
+                                    in nsIPrincipal aCurrentPrincipal,
+                                    in boolean aIsSubframe);
 };
diff --git a/toolkit/xre/nsAppRunner.cpp b/toolkit/xre/nsAppRunner.cpp
index a3290c0fb111..5b0675db9337 100644
--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -700,11 +700,12 @@ nsXULAppInfo::GetUniqueProcessID(uint64_t* aResult) {
 }
 
 NS_IMETHODIMP
-nsXULAppInfo::GetRemoteType(nsACString& aRemoteType) {
+nsXULAppInfo::GetRemoteType(nsAString& aRemoteType) {
   if (XRE_IsContentProcess()) {
-    aRemoteType = ContentChild::GetSingleton()->GetRemoteType();
+    ContentChild* cc = ContentChild::GetSingleton();
+    aRemoteType.Assign(cc->GetRemoteType());
   } else {
-    aRemoteType = NOT_REMOTE_TYPE;
+    SetDOMStringToNull(aRemoteType);
   }
 
   return NS_OK;
@@ -842,8 +843,8 @@ NS_IMETHODIMP
 nsXULAppInfo::EnsureContentProcess() {
   if (!XRE_IsParentProcess()) return NS_ERROR_NOT_AVAILABLE;
 
-  RefPtr<ContentParent> unused =
-      ContentParent::GetNewOrUsedBrowserProcess(nullptr, DEFAULT_REMOTE_TYPE);
+  RefPtr<ContentParent> unused = ContentParent::GetNewOrUsedBrowserProcess(
+      nullptr, NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE));
   return NS_OK;
 }
 
diff --git a/toolkit/xre/nsEmbedFunctions.cpp b/toolkit/xre/nsEmbedFunctions.cpp
index 68ac80315709..f3a2e79329fa 100644
--- a/toolkit/xre/nsEmbedFunctions.cpp
+++ b/toolkit/xre/nsEmbedFunctions.cpp
@@ -947,8 +947,8 @@ TestShellParent* GetOrCreateTestShellParent() {
     // this and you're sure you wouldn't be better off writing a "browser"
     // chrome mochitest where you can have multiple types of content
     // processes.
-    RefPtr<ContentParent> parent =
-        ContentParent::GetNewOrUsedBrowserProcess(nullptr, DEFAULT_REMOTE_TYPE);
+    RefPtr<ContentParent> parent = ContentParent::GetNewOrUsedBrowserProcess(
+        nullptr, NS_LITERAL_STRING_FROM_CSTRING(DEFAULT_REMOTE_TYPE));
     parent.forget(&gContentParent);
   } else if (!gContentParent->IsAlive()) {
     return nullptr;
diff --git a/tools/fuzzing/ipc/ProtocolFuzzer.cpp b/tools/fuzzing/ipc/ProtocolFuzzer.cpp
index e2d7aae96d3d..8d2bd9b8404c 100644
--- a/tools/fuzzing/ipc/ProtocolFuzzer.cpp
+++ b/tools/fuzzing/ipc/ProtocolFuzzer.cpp
@@ -21,7 +21,7 @@ nsTArray<nsCString> LoadIPCMessageBlacklist(const char* aPath) {
 }
 
 mozilla::dom::ContentParent* ProtocolFuzzerHelper::CreateContentParent(
-    const nsACString& aRemoteType) {
+    const nsAString& aRemoteType) {
   auto* cp = new mozilla::dom::ContentParent(aRemoteType);
   // TODO: this duplicates MessageChannel::Open
   cp->GetIPCChannel()->mWorkerThread = GetCurrentSerialEventTarget();
diff --git a/tools/fuzzing/ipc/ProtocolFuzzer.h b/tools/fuzzing/ipc/ProtocolFuzzer.h
index f57852038ae8..88eea8ffdb90 100644
--- a/tools/fuzzing/ipc/ProtocolFuzzer.h
+++ b/tools/fuzzing/ipc/ProtocolFuzzer.h
@@ -19,7 +19,7 @@ namespace ipc {
 class ProtocolFuzzerHelper {
  public:
   static mozilla::dom::ContentParent* CreateContentParent(
-      const nsACString& aRemoteType);
+      const nsAString& aRemoteType);
 
   static void CompositorBridgeParentSetup();
 
diff --git a/uriloader/exthandler/nsExternalProtocolHandler.cpp b/uriloader/exthandler/nsExternalProtocolHandler.cpp
index 64a585df8d7e..e9eab96acf64 100644
--- a/uriloader/exthandler/nsExternalProtocolHandler.cpp
+++ b/uriloader/exthandler/nsExternalProtocolHandler.cpp
@@ -426,7 +426,7 @@ NS_IMETHODIMP nsExtProtocolChannel::Delete() {
   return NS_OK;
 }
 
-NS_IMETHODIMP nsExtProtocolChannel::GetRemoteType(nsACString& aRemoteType) {
+NS_IMETHODIMP nsExtProtocolChannel::GetRemoteType(nsAString& aRemoteType) {
   return NS_ERROR_NOT_IMPLEMENTED;
 }
 
diff --git a/widget/ProcInfo.h b/widget/ProcInfo.h
index 0076603adfe4..4628b9e81650 100644
--- a/widget/ProcInfo.h
+++ b/widget/ProcInfo.h
@@ -68,7 +68,7 @@ struct ProcInfo {
   // Process type
   ProcType type;
   // Origin, if any
-  nsCString origin;
+  nsString origin;
   // Process filename (without the path name).
   nsString filename;
   // VMS in bytes.
@@ -94,12 +94,12 @@ typedef MozPromise<ProcInfo, nsresult, true> ProcInfoPromise;
 #ifdef XP_MACOSX
 RefPtr<ProcInfoPromise> GetProcInfo(base::ProcessId pid, int32_t childId,
                                     const ProcType& processType,
-                                    const nsACString& origin,
+                                    const nsAString& origin,
                                     mach_port_t aChildTask = MACH_PORT_NULL);
 #else
 RefPtr<ProcInfoPromise> GetProcInfo(base::ProcessId pid, int32_t childId,
                                     const ProcType& processType,
-                                    const nsACString& origin);
+                                    const nsAString& origin);
 #endif
 
 }  // namespace mozilla
diff --git a/widget/android/ProcInfo.cpp b/widget/android/ProcInfo.cpp
index 0bcdcb625cce..7e054aaa4446 100644
--- a/widget/android/ProcInfo.cpp
+++ b/widget/android/ProcInfo.cpp
@@ -11,7 +11,7 @@ namespace mozilla {
 
 RefPtr<ProcInfoPromise> GetProcInfo(base::ProcessId pid, int32_t childId,
                                     const ProcType& type,
-                                    const nsACString& origin) {
+                                    const nsAString& origin) {
   // Not implemented on Android.
   return ProcInfoPromise::CreateAndReject(NS_ERROR_NOT_IMPLEMENTED, __func__);
 }
diff --git a/widget/cocoa/ProcInfo.mm b/widget/cocoa/ProcInfo.mm
index 6dc233dd0ba5..8cb4df477161 100644
--- a/widget/cocoa/ProcInfo.mm
+++ b/widget/cocoa/ProcInfo.mm
@@ -20,7 +20,7 @@
 namespace mozilla {
 
 RefPtr<ProcInfoPromise> GetProcInfo(base::ProcessId pid, int32_t childId, const ProcType& type,
-                                    const nsACString& origin, mach_port_t aChildTask) {
+                                    const nsAString& origin, mach_port_t aChildTask) {
   auto holder = MakeUnique<MozPromiseHolder<ProcInfoPromise>>();
   RefPtr<ProcInfoPromise> promise = holder->Ensure(__func__);
 
@@ -33,7 +33,7 @@ RefPtr<ProcInfoPromise> GetProcInfo(base::ProcessId pid, int32_t childId, const
   }
 
   // Ensure that the string is still alive when `ResolveGetProcInfo` is called.
-  nsCString originCopy(origin);
+  nsString originCopy(origin);
   auto ResolveGetProcinfo = [holder = std::move(holder), pid, type,
                              originCopy = std::move(originCopy), childId, aChildTask]() {
     ProcInfo info;
diff --git a/widget/gtk/ProcInfo.cpp b/widget/gtk/ProcInfo.cpp
index 857f45245fc7..1538b561b4c2 100644
--- a/widget/gtk/ProcInfo.cpp
+++ b/widget/gtk/ProcInfo.cpp
@@ -211,7 +211,7 @@ class ThreadInfoReader final : public StatReader {
 
 RefPtr<ProcInfoPromise> GetProcInfo(base::ProcessId pid, int32_t childId,
                                     const ProcType& type,
-                                    const nsACString& origin) {
+                                    const nsAString& origin) {
   auto holder = MakeUnique<MozPromiseHolder<ProcInfoPromise>>();
   RefPtr<ProcInfoPromise> promise = holder->Ensure(__func__);
   nsresult rv = NS_OK;
@@ -224,7 +224,7 @@ RefPtr<ProcInfoPromise> GetProcInfo(base::ProcessId pid, int32_t childId,
   }
 
   // Ensure that the string is still alive when the runnable is called.
-  nsCString originCopy(origin);
+  nsString originCopy(origin);
   RefPtr<nsIRunnable> r = NS_NewRunnableFunction(
       __func__, [holder = std::move(holder), pid, type,
                  originCopy = std::move(originCopy), childId]() {
diff --git a/widget/windows/ProcInfo.cpp b/widget/windows/ProcInfo.cpp
index 1050bdd7064b..ee13aa65ba07 100644
--- a/widget/windows/ProcInfo.cpp
+++ b/widget/windows/ProcInfo.cpp
@@ -77,7 +77,7 @@ void AppendThreads(ProcInfo* info) {
 
 RefPtr<ProcInfoPromise> GetProcInfo(base::ProcessId pid, int32_t childId,
                                     const ProcType& type,
-                                    const nsACString& origin) {
+                                    const nsAString& origin) {
   auto holder = MakeUnique<MozPromiseHolder<ProcInfoPromise>>();
   RefPtr<ProcInfoPromise> promise = holder->Ensure(__func__);
 
@@ -91,7 +91,7 @@ RefPtr<ProcInfoPromise> GetProcInfo(base::ProcessId pid, int32_t childId,
   }
 
   // Ensure that the string is still alive when `ResolveGetProcInfo` is called.
-  nsCString originCopy(origin);
+  nsString originCopy(origin);
   RefPtr<nsIRunnable> r = NS_NewRunnableFunction(
       __func__,
       [holder = std::move(holder), originCopy = std::move(originCopy), pid,
diff --git a/xpcom/system/nsIXULRuntime.idl b/xpcom/system/nsIXULRuntime.idl
index 28eab662effe..47b6cb8e3133 100644
--- a/xpcom/system/nsIXULRuntime.idl
+++ b/xpcom/system/nsIXULRuntime.idl
@@ -112,7 +112,7 @@ interface nsIXULRuntime : nsISupports
    * a URI if Fission is enabled, so don't use it for any kind of
    * telemetry.
    */
-  readonly attribute AUTF8String remoteType;
+  readonly attribute AString remoteType;
 
   /**
    * If true, browser tabs may be opened by default in a different process