diff --git a/dom/file/MutableBlobStorage.cpp b/dom/file/MutableBlobStorage.cpp
index 1549880d646f..6050a2af2e62 100644
--- a/dom/file/MutableBlobStorage.cpp
+++ b/dom/file/MutableBlobStorage.cpp
@@ -46,6 +46,7 @@ public:
   Run() override
   {
     MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(mBlobStorage);
     mCallback->BlobStoreCompleted(mBlobStorage, mBlob, mRv);
     mCallback = nullptr;
     mBlob = nullptr;
@@ -55,10 +56,11 @@ public:
 private:
   ~BlobCreationDoneRunnable()
   {
+    MOZ_ASSERT(mBlobStorage);
     // If something when wrong, we still have to release these objects in the
     // correct thread.
-    NS_ReleaseOnMainThread(mCallback.forget());
-    NS_ReleaseOnMainThread(mBlob.forget());
+    NS_ProxyRelease(mBlobStorage->EventTarget(), mCallback.forget());
+    NS_ProxyRelease(mBlobStorage->EventTarget(), mBlob.forget());
   }
 
   RefPtr<MutableBlobStorage> mBlobStorage;
@@ -120,6 +122,7 @@ public:
   {
     MOZ_ASSERT(!NS_IsMainThread());
     MOZ_ASSERT(XRE_IsParentProcess());
+    MOZ_ASSERT(mBlobStorage);
 
     PRFileDesc* tempFD = nullptr;
     nsresult rv = NS_OpenAnonymousTemporaryFile(&tempFD);
@@ -128,7 +131,8 @@ public:
     }
 
     // The ownership of the tempFD is moved to the FileCreatedRunnable.
-    return NS_DispatchToMainThread(new FileCreatedRunnable(mBlobStorage, tempFD));
+    return mBlobStorage->EventTarget()->Dispatch(
+      new FileCreatedRunnable(mBlobStorage, tempFD), NS_DISPATCH_NORMAL);
   }
 
 private:
@@ -196,11 +200,13 @@ public:
   Run() override
   {
     MOZ_ASSERT(!NS_IsMainThread());
+    MOZ_ASSERT(mBlobStorage);
 
     int32_t written = PR_Write(mFD, mData, mLength);
     if (NS_WARN_IF(written < 0 || uint32_t(written) != mLength)) {
-      return NS_DispatchToMainThread(
-        new ErrorPropagationRunnable(mBlobStorage, NS_ERROR_FAILURE));
+      return mBlobStorage->EventTarget()->Dispatch(
+        new ErrorPropagationRunnable(mBlobStorage, NS_ERROR_FAILURE),
+        NS_DISPATCH_NORMAL);
     }
 
     return NS_OK;
@@ -275,12 +281,14 @@ public:
     , mCallback(aCallback)
   {
     MOZ_ASSERT(!NS_IsMainThread());
+    MOZ_ASSERT(aBlobStorage);
   }
 
   NS_IMETHOD
   Run() override
   {
     MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(mBlobStorage);
     mBlobStorage->CreateBlobAndRespond(mParent.forget(), mContentType,
                                        mCallback.forget());
     return NS_OK;
@@ -289,10 +297,11 @@ public:
 private:
   ~CreateBlobRunnable()
   {
+    MOZ_ASSERT(mBlobStorage);
     // If something when wrong, we still have to release data in the correct
     // thread.
-    NS_ReleaseOnMainThread(mParent.forget());
-    NS_ReleaseOnMainThread(mCallback.forget());
+    NS_ProxyRelease(mBlobStorage->EventTarget(), mParent.forget());
+    NS_ProxyRelease(mBlobStorage->EventTarget(), mCallback.forget());
   }
 
   RefPtr<MutableBlobStorage> mBlobStorage;
@@ -324,19 +333,21 @@ public:
   Run() override
   {
     MOZ_ASSERT(!NS_IsMainThread());
+    MOZ_ASSERT(mBlobStorage);
     RefPtr<Runnable> runnable =
       new CreateBlobRunnable(mBlobStorage, mParent.forget(),
                              mContentType, mCallback.forget());
-    return NS_DispatchToMainThread(runnable);
+    return mBlobStorage->EventTarget()->Dispatch(runnable, NS_DISPATCH_NORMAL);
   }
 
 private:
   ~LastRunnable()
   {
+    MOZ_ASSERT(mBlobStorage);
     // If something when wrong, we still have to release data in the correct
     // thread.
-    NS_ReleaseOnMainThread(mParent.forget());
-    NS_ReleaseOnMainThread(mCallback.forget());
+    NS_ProxyRelease(mBlobStorage->EventTarget(), mParent.forget());
+    NS_ProxyRelease(mBlobStorage->EventTarget(), mCallback.forget());
   }
 
   RefPtr<MutableBlobStorage> mBlobStorage;
@@ -347,15 +358,23 @@ private:
 
 } // anonymous namespace
 
-MutableBlobStorage::MutableBlobStorage(MutableBlobStorageType aType)
+MutableBlobStorage::MutableBlobStorage(MutableBlobStorageType aType,
+                                       nsIEventTarget* aEventTarget)
   : mData(nullptr)
   , mDataLen(0)
   , mDataBufferLen(0)
   , mStorageState(aType == eOnlyInMemory ? eKeepInMemory : eInMemory)
   , mFD(nullptr)
   , mErrorResult(NS_OK)
+  , mEventTarget(aEventTarget)
 {
   MOZ_ASSERT(NS_IsMainThread());
+
+  if (!mEventTarget) {
+    mEventTarget = do_GetMainThread();
+  }
+
+  MOZ_ASSERT(mEventTarget);
 }
 
 MutableBlobStorage::~MutableBlobStorage()
@@ -391,7 +410,7 @@ MutableBlobStorage::GetBlobWhenReady(nsISupports* aParent,
     if (NS_FAILED(mErrorResult)) {
       RefPtr<Runnable> runnable =
         new BlobCreationDoneRunnable(this, aCallback, nullptr, mErrorResult);
-      NS_DispatchToMainThread(runnable.forget());
+      EventTarget()->Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
       return 0;
     }
 
@@ -421,7 +440,7 @@ MutableBlobStorage::GetBlobWhenReady(nsISupports* aParent,
   RefPtr<BlobCreationDoneRunnable> runnable =
     new BlobCreationDoneRunnable(this, aCallback, blob, NS_OK);
 
-  nsresult error = NS_DispatchToMainThread(runnable);
+  nsresult error = EventTarget()->Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
   if (NS_WARN_IF(NS_FAILED(error))) {
     return 0;
   }
@@ -539,7 +558,8 @@ MutableBlobStorage::MaybeCreateTemporaryFile()
       AsyncOpenAnonymousTemporaryFile([self](PRFileDesc* prfile) {
         if (prfile) {
           // The ownership of the prfile is moved to the FileCreatedRunnable.
-          NS_DispatchToMainThread(new FileCreatedRunnable(self, prfile));
+          self->EventTarget()->Dispatch(
+            new FileCreatedRunnable(self, prfile), NS_DISPATCH_NORMAL);
         }
       });
   }
diff --git a/dom/file/MutableBlobStorage.h b/dom/file/MutableBlobStorage.h
index 422f941a6902..a948918a1ceb 100644
--- a/dom/file/MutableBlobStorage.h
+++ b/dom/file/MutableBlobStorage.h
@@ -10,6 +10,8 @@
 #include "mozilla/RefPtr.h"
 #include "prio.h"
 
+class nsIEventTarget;
+
 namespace mozilla {
 
 class TaskQueue;
@@ -42,7 +44,8 @@ public:
     eCouldBeInTemporaryFile,
   };
 
-  explicit MutableBlobStorage(MutableBlobStorageType aType);
+  explicit MutableBlobStorage(MutableBlobStorageType aType,
+                              nsIEventTarget* aEventTarget = nullptr);
 
   nsresult Append(const void* aData, uint32_t aLength);
 
@@ -61,6 +64,12 @@ public:
 
   void ErrorPropagated(nsresult aRv);
 
+  nsIEventTarget* EventTarget()
+  {
+    MOZ_ASSERT(mEventTarget);
+    return mEventTarget;
+  }
+
 private:
   ~MutableBlobStorage();
 
@@ -93,6 +102,7 @@ private:
   nsresult mErrorResult;
 
   RefPtr<TaskQueue> mTaskQueue;
+  nsCOMPtr<nsIEventTarget> mEventTarget;
 };
 
 } // namespace dom
diff --git a/dom/file/MutableBlobStreamListener.cpp b/dom/file/MutableBlobStreamListener.cpp
index 6769ad3e66f5..152429fd0add 100644
--- a/dom/file/MutableBlobStreamListener.cpp
+++ b/dom/file/MutableBlobStreamListener.cpp
@@ -12,14 +12,22 @@ namespace dom {
 MutableBlobStreamListener::MutableBlobStreamListener(MutableBlobStorage::MutableBlobStorageType aStorageType,
                                                      nsISupports* aParent,
                                                      const nsACString& aContentType,
-                                                     MutableBlobStorageCallback* aCallback)
+                                                     MutableBlobStorageCallback* aCallback,
+                                                     nsIEventTarget* aEventTarget)
   : mCallback(aCallback)
   , mParent(aParent)
   , mStorageType(aStorageType)
   , mContentType(aContentType)
+  , mEventTarget(aEventTarget)
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(aCallback);
+
+  if (!mEventTarget) {
+    mEventTarget = do_GetMainThread();
+  }
+
+  MOZ_ASSERT(mEventTarget);
 }
 
 MutableBlobStreamListener::~MutableBlobStreamListener()
@@ -36,8 +44,9 @@ MutableBlobStreamListener::OnStartRequest(nsIRequest* aRequest, nsISupports* aCo
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(!mStorage);
+  MOZ_ASSERT(mEventTarget);
 
-  mStorage = new MutableBlobStorage(mStorageType);
+  mStorage = new MutableBlobStorage(mStorageType, mEventTarget);
   return NS_OK;
 }
 
diff --git a/dom/file/MutableBlobStreamListener.h b/dom/file/MutableBlobStreamListener.h
index 1dc044c61d83..47b36f044d8c 100644
--- a/dom/file/MutableBlobStreamListener.h
+++ b/dom/file/MutableBlobStreamListener.h
@@ -10,6 +10,8 @@
 #include "nsIStreamListener.h"
 #include "mozilla/dom/MutableBlobStorage.h"
 
+class nsIEventTarget;
+
 namespace mozilla {
 namespace dom {
 
@@ -24,7 +26,8 @@ public:
   MutableBlobStreamListener(MutableBlobStorage::MutableBlobStorageType aType,
                             nsISupports* aParent,
                             const nsACString& aContentType,
-                            MutableBlobStorageCallback* aCallback);
+                            MutableBlobStorageCallback* aCallback,
+                            nsIEventTarget* aEventTarget = nullptr);
 
 private:
   ~MutableBlobStreamListener();
@@ -40,6 +43,7 @@ private:
   nsCOMPtr<nsISupports> mParent;
   MutableBlobStorage::MutableBlobStorageType mStorageType;
   nsCString mContentType;
+  nsCOMPtr<nsIEventTarget> mEventTarget;
 };
 
 } // namespace dom