diff --git a/dom/script/ModuleLoader.cpp b/dom/script/ModuleLoader.cpp
index 0b94a7f6d67a..d8d084e379cf 100644
--- a/dom/script/ModuleLoader.cpp
+++ b/dom/script/ModuleLoader.cpp
@@ -460,6 +460,12 @@ nsresult ModuleLoader::CompileOrFinishModuleScript(
       return NS_ERROR_FAILURE;
     }
 
+    if (ScriptLoader::ShouldCacheBytecode(aRequest)) {
+      if (!JS::StartIncrementalEncoding(aCx, std::move(stencil))) {
+        return NS_ERROR_FAILURE;
+      }
+    }
+
     return NS_OK;
   }
 
@@ -487,6 +493,12 @@ nsresult ModuleLoader::CompileOrFinishModuleScript(
     return NS_ERROR_FAILURE;
   }
 
+  if (ScriptLoader::ShouldCacheBytecode(aRequest)) {
+    if (!JS::StartIncrementalEncoding(aCx, std::move(stencil))) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+
   return NS_OK;
 }
 
diff --git a/dom/script/ScriptLoader.cpp b/dom/script/ScriptLoader.cpp
index ecc6703a97b3..bee9b47cf1f1 100644
--- a/dom/script/ScriptLoader.cpp
+++ b/dom/script/ScriptLoader.cpp
@@ -20,6 +20,7 @@
 #include "js/loader/LoadedScript.h"
 #include "js/loader/ModuleLoadRequest.h"
 #include "js/MemoryFunctions.h"
+#include "js/Modules.h"
 #include "js/OffThreadScriptCompilation.h"
 #include "js/PropertyAndElement.h"  // JS_DefineProperty
 #include "js/Realm.h"
@@ -589,6 +590,7 @@ nsresult ScriptLoader::StartLoadInternal(ScriptLoadRequest* aRequest,
   nsCOMPtr<nsICacheInfoChannel> cic(do_QueryInterface(channel));
   if (cic && StaticPrefs::dom_script_loader_bytecode_cache_enabled() &&
       // Bug 1436400: no bytecode cache support for modules yet.
+      // TODO: Remove this also to enable bytecode encoding.
       !aRequest->IsModuleRequest()) {
     MOZ_ASSERT(!aRequest->GetLoadContext()->GetWebExtGlobal(),
                "Can not bytecode cache WebExt code");
@@ -2127,6 +2129,9 @@ nsresult ScriptLoader::CompileOrDecodeClassicScript(
 
 /* static */
 nsCString& ScriptLoader::BytecodeMimeTypeFor(ScriptLoadRequest* aRequest) {
+  if (aRequest->IsModuleRequest()) {
+    return nsContentUtils::JSModuleBytecodeMimeType();
+  }
   return nsContentUtils::JSScriptBytecodeMimeType();
 }
 
@@ -2148,6 +2153,7 @@ nsresult ScriptLoader::MaybePrepareForBytecodeEncodingAfterExecute(
     //       first encode.
     MOZ_ASSERT(aRequest->mBytecodeOffset == aRequest->mScriptBytecode.length());
     RegisterForBytecodeEncoding(aRequest);
+    MOZ_ASSERT(IsAlreadyHandledForBytecodeEncodingPreparation(aRequest));
 
     return aRv;
   }
@@ -2157,6 +2163,54 @@ nsresult ScriptLoader::MaybePrepareForBytecodeEncodingAfterExecute(
   TRACE_FOR_TEST_NONE(aRequest->GetLoadContext()->GetScriptElement(),
                       "scriptloader_no_encode");
   aRequest->mCacheInfo = nullptr;
+  MOZ_ASSERT(IsAlreadyHandledForBytecodeEncodingPreparation(aRequest));
+
+  return aRv;
+}
+
+bool ScriptLoader::IsAlreadyHandledForBytecodeEncodingPreparation(
+    ScriptLoadRequest* aRequest) {
+  return aRequest->isInList() || !aRequest->mCacheInfo;
+}
+
+void ScriptLoader::MaybePrepareModuleForBytecodeEncodingBeforeExecute(
+    JSContext* aCx, ModuleLoadRequest* aRequest) {
+  {
+    ModuleScript* moduleScript = aRequest->mModuleScript;
+    JS::Rooted<JSObject*> module(aCx, moduleScript->ModuleRecord());
+
+    if (JS::IsModuleEvaluated(module)) {
+      // This module is already evaluated, and all imported modules should also
+      // already be evaluated.
+      return;
+    }
+
+    if (aRequest->IsMarkedForBytecodeEncoding()) {
+      // This module is imported multiple times, and already marked.
+      return;
+    }
+
+    JS::Rooted<JSScript*> script(aCx, JS::GetModuleScript(module));
+    MaybePrepareForBytecodeEncodingBeforeExecute(aRequest, script);
+  }
+
+  for (ModuleLoadRequest* childRequest : aRequest->mImports) {
+    MaybePrepareModuleForBytecodeEncodingBeforeExecute(aCx, childRequest);
+  }
+}
+
+nsresult ScriptLoader::MaybePrepareModuleForBytecodeEncodingAfterExecute(
+    ModuleLoadRequest* aRequest, nsresult aRv) {
+  if (IsAlreadyHandledForBytecodeEncodingPreparation(aRequest)) {
+    // This module is imported multiple times and already handled.
+    return aRv;
+  }
+
+  aRv = MaybePrepareForBytecodeEncodingAfterExecute(aRequest, aRv);
+
+  for (ModuleLoadRequest* childRequest : aRequest->mImports) {
+    aRv = MaybePrepareModuleForBytecodeEncodingAfterExecute(childRequest, aRv);
+  }
 
   return aRv;
 }
@@ -2338,7 +2392,6 @@ void ScriptLoader::EncodeBytecode() {
   RefPtr<ScriptLoadRequest> request;
   while (!mBytecodeEncodingQueue.isEmpty()) {
     request = mBytecodeEncodingQueue.StealFirst();
-    MOZ_ASSERT(!request->IsModuleRequest());
     MOZ_ASSERT(!request->GetLoadContext()->GetWebExtGlobal(),
                "Not handling global above");
     EncodeRequestBytecode(aes.cx(), request);
@@ -2441,7 +2494,6 @@ void ScriptLoader::GiveUpBytecodeEncoding() {
     LOG(("ScriptLoadRequest (%p): Cannot serialize bytecode", request.get()));
     TRACE_FOR_TEST_NONE(request->GetLoadContext()->GetScriptElement(),
                         "scriptloader_bytecode_failed");
-    MOZ_ASSERT(!request->IsModuleRequest());
     MOZ_ASSERT(!request->GetLoadContext()->GetWebExtGlobal());
 
     if (aes.isSome()) {
diff --git a/dom/script/ScriptLoader.h b/dom/script/ScriptLoader.h
index a85caf77c89c..6471b5308267 100644
--- a/dom/script/ScriptLoader.h
+++ b/dom/script/ScriptLoader.h
@@ -573,6 +573,17 @@ class ScriptLoader final : public JS::loader::ScriptLoaderInterface {
   nsresult MaybePrepareForBytecodeEncodingAfterExecute(
       ScriptLoadRequest* aRequest, nsresult aRv);
 
+  // Returns true if MaybePrepareForBytecodeEncodingAfterExecute is called
+  // for given script load request.
+  bool IsAlreadyHandledForBytecodeEncodingPreparation(
+      ScriptLoadRequest* aRequest);
+
+  void MaybePrepareModuleForBytecodeEncodingBeforeExecute(
+      JSContext* aCx, ModuleLoadRequest* aRequest) override;
+
+  nsresult MaybePrepareModuleForBytecodeEncodingAfterExecute(
+      ModuleLoadRequest* aRequest, nsresult aRv) override;
+
   // Implements https://html.spec.whatwg.org/#run-a-classic-script
   nsresult EvaluateScript(nsIGlobalObject* aGlobalObject,
                           ScriptLoadRequest* aRequest);
@@ -590,7 +601,7 @@ class ScriptLoader final : public JS::loader::ScriptLoaderInterface {
    * no more script have to be processed.  If all conditions are met, queue an
    * event to encode all the bytecode and save them on the cache.
    */
-  void MaybeTriggerBytecodeEncoding();
+  void MaybeTriggerBytecodeEncoding() override;
 
   /**
    * Iterate over all script load request and save the bytecode of executed
diff --git a/js/loader/ModuleLoaderBase.cpp b/js/loader/ModuleLoaderBase.cpp
index 78002c666dd4..ef5b47d49cb1 100644
--- a/js/loader/ModuleLoaderBase.cpp
+++ b/js/loader/ModuleLoaderBase.cpp
@@ -777,6 +777,8 @@ nsresult ModuleLoaderBase::EvaluateModule(nsIGlobalObject* aGlobalObject,
 
   JS::Rooted<JS::Value> rval(cx);
 
+  mLoader->MaybePrepareModuleForBytecodeEncodingBeforeExecute(cx, request);
+
   rv = nsJSUtils::ModuleEvaluate(cx, module, &rval);
 
   if (NS_SUCCEEDED(rv)) {
@@ -814,11 +816,10 @@ nsresult ModuleLoaderBase::EvaluateModule(nsIGlobalObject* aGlobalObject,
     }
   }
 
-  if (aRequest->HasLoadContext()) {
-    TRACE_FOR_TEST_NONE(aRequest->GetLoadContext()->GetScriptElement(),
-                        "scriptloader_no_encode");
-  }
-  aRequest->mCacheInfo = nullptr;
+  rv = mLoader->MaybePrepareModuleForBytecodeEncodingAfterExecute(request, rv);
+
+  mLoader->MaybeTriggerBytecodeEncoding();
+
   return rv;
 }
 
diff --git a/js/loader/ModuleLoaderBase.h b/js/loader/ModuleLoaderBase.h
index d7438cd06ead..58db090a0de3 100644
--- a/js/loader/ModuleLoaderBase.h
+++ b/js/loader/ModuleLoaderBase.h
@@ -70,6 +70,14 @@ class ScriptLoaderInterface : public nsISupports {
       JSContext* cx, ScriptLoadRequest* aRequest,
       JS::Handle<JSObject*> aScopeChain, JS::CompileOptions* aOptions,
       JS::MutableHandle<JSScript*> aIntroductionScript) = 0;
+
+  virtual void MaybePrepareModuleForBytecodeEncodingBeforeExecute(
+      JSContext* aCx, ModuleLoadRequest* aRequest) = 0;
+
+  virtual nsresult MaybePrepareModuleForBytecodeEncodingAfterExecute(
+      ModuleLoadRequest* aRequest, nsresult aRv) = 0;
+
+  virtual void MaybeTriggerBytecodeEncoding() = 0;
 };
 
 class ModuleLoaderBase : public nsISupports {