diff --git a/dom/script/ModuleScript.cpp b/dom/script/ModuleScript.cpp
index a8d6ce5343..35dec499c8 100644
--- a/dom/script/ModuleScript.cpp
+++ b/dom/script/ModuleScript.cpp
@@ -16,45 +16,86 @@
 namespace mozilla {
 namespace dom {
 
-// A single module script.  May be used to satisfy multiple load requests.
+//////////////////////////////////////////////////////////////
+// LoadedScript
+//////////////////////////////////////////////////////////////
 
-NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ModuleScript)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(LoadedScript)
 NS_INTERFACE_MAP_END
 
-NS_IMPL_CYCLE_COLLECTION_CLASS(ModuleScript)
+NS_IMPL_CYCLE_COLLECTION_CLASS(LoadedScript)
 
-NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(ModuleScript)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(LoadedScript)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mLoader)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mFetchOptions)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mBaseURL)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(LoadedScript)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mLoader)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFetchOptions)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(LoadedScript)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(LoadedScript)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(LoadedScript)
+
+LoadedScript::LoadedScript(ScriptKind aKind, ScriptLoader* aLoader,
+                           ScriptFetchOptions* aFetchOptions, nsIURI* aBaseURL)
+    : mKind(aKind),
+      mLoader(aLoader),
+      mFetchOptions(aFetchOptions),
+      mBaseURL(aBaseURL) 
+{
+  MOZ_ASSERT(mLoader);
+  MOZ_ASSERT(mFetchOptions);
+  MOZ_ASSERT(mBaseURL);
+}
+
+LoadedScript::~LoadedScript() { DropJSObjects(this); }
+
+//////////////////////////////////////////////////////////////
+// ClassicScript
+//////////////////////////////////////////////////////////////
+
+ClassicScript::ClassicScript(ScriptLoader* aLoader,
+                             ScriptFetchOptions* aFetchOptions,
+                             nsIURI* aBaseURL)
+    : LoadedScript(ScriptKind::Classic, aLoader, aFetchOptions, aBaseURL) {}
+
+//////////////////////////////////////////////////////////////
+// ModuleScript
+//////////////////////////////////////////////////////////////
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ModuleScript)
+NS_INTERFACE_MAP_END_INHERITING(LoadedScript)
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(ModuleScript)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(ModuleScript, LoadedScript)
   tmp->UnlinkModuleRecord();
   tmp->mParseError.setUndefined();
   tmp->mErrorToRethrow.setUndefined();
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
-NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(ModuleScript)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mLoader)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFetchOptions)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(ModuleScript, LoadedScript)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
-NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(ModuleScript)
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(ModuleScript, LoadedScript)
   NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mModuleRecord)
   NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mParseError)
   NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mErrorToRethrow)
 NS_IMPL_CYCLE_COLLECTION_TRACE_END
 
-NS_IMPL_CYCLE_COLLECTING_ADDREF(ModuleScript)
-NS_IMPL_CYCLE_COLLECTING_RELEASE(ModuleScript)
+NS_IMPL_ADDREF_INHERITED(ModuleScript, LoadedScript)
+NS_IMPL_RELEASE_INHERITED(ModuleScript, LoadedScript)
 
 ModuleScript::ModuleScript(ScriptLoader* aLoader,
                            ScriptFetchOptions* aFetchOptions, nsIURI* aBaseURL)
-    : mLoader(aLoader),
-      mFetchOptions(aFetchOptions),
-      mBaseURL(aBaseURL) {
-  MOZ_ASSERT(mLoader);
-  MOZ_ASSERT(mFetchOptions);
-  MOZ_ASSERT(mBaseURL);
-  MOZ_ASSERT(!mModuleRecord);
+    : LoadedScript(ScriptKind::Module, aLoader, aFetchOptions, aBaseURL) {
+  MOZ_ASSERT(!ModuleRecord());
   MOZ_ASSERT(!HasParseError());
   MOZ_ASSERT(!HasErrorToRethrow());
 }
@@ -77,21 +118,21 @@ ModuleScript::~ModuleScript()
 {
   // The object may be destroyed without being unlinked first.
   UnlinkModuleRecord();
-  DropJSObjects(this);
 }
 
 void
 ModuleScript::SetModuleRecord(JS::Handle<JSObject*> aModuleRecord)
 {
   MOZ_ASSERT(!mModuleRecord);
-  MOZ_ASSERT(!HasParseError());
-  MOZ_ASSERT(!HasErrorToRethrow());
+  MOZ_ASSERT_IF(IsModuleScript(), !AsModuleScript()->HasParseError());
+  MOZ_ASSERT_IF(IsModuleScript(), !AsModuleScript()->HasErrorToRethrow());
 
   mModuleRecord = aModuleRecord;
 
   // Make module's host defined field point to this object and
   // increment our reference count. This is decremented by
   // UnlinkModuleRecord() above.
+  MOZ_ASSERT(JS::GetModulePrivate(mModuleRecord).isUndefined());
   JS::SetModulePrivate(mModuleRecord, JS::PrivateValue(this));
   HoldJSObjects(this);
 }
@@ -125,7 +166,7 @@ ModuleScript::SetErrorToRethrow(const JS::Value& aError)
 
   // This is only called after SetModuleRecord() or SetParseError() so we don't
   // need to call HoldJSObjects() here.
-  MOZ_ASSERT(mModuleRecord || HasParseError());
+  MOZ_ASSERT(ModuleRecord() || HasParseError());
 
   mErrorToRethrow = aError;
 }
diff --git a/dom/script/ModuleScript.h b/dom/script/ModuleScript.h
index 8901932868..95b4edbb94 100644
--- a/dom/script/ModuleScript.h
+++ b/dom/script/ModuleScript.h
@@ -9,6 +9,7 @@
 #include "nsCOMPtr.h"
 #include "nsCycleCollectionParticipant.h"
 #include "jsapi.h"
+#include "ScriptLoader.h"
 
 class nsIURI;
 
@@ -19,11 +20,49 @@ class ScriptLoader;
 
 void HostFinalizeTopLevelScript(JSFreeOp* aFop, const JS::Value& aPrivate);
 
-class ModuleScript final : public nsISupports
+class ClassicScript;
+class ModuleScript;
+
+class LoadedScript : public nsISupports
 {
+  ScriptKind mKind;
   RefPtr<ScriptLoader> mLoader;
   RefPtr<ScriptFetchOptions> mFetchOptions;
   nsCOMPtr<nsIURI> mBaseURL;
+ 
+  protected:
+   LoadedScript(ScriptKind aKind, ScriptLoader* aLoader,
+               ScriptFetchOptions* aFetchOptions, nsIURI* aBaseURL);
+
+  virtual ~LoadedScript();
+
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(LoadedScript)
+
+  bool IsModuleScript() const { return mKind == ScriptKind::Module; }
+
+  inline ClassicScript* AsClassicScript();
+  inline ModuleScript* AsModuleScript();
+
+  ScriptLoader* Loader() const { return mLoader; }
+  ScriptFetchOptions* FetchOptions() const { return mFetchOptions; }
+  nsIURI* BaseURL() const { return mBaseURL; }
+};
+
+class ClassicScript final : public LoadedScript
+{
+  ~ClassicScript() = default;
+
+ public:
+  ClassicScript(ScriptLoader* aLoader, ScriptFetchOptions* aFetchOptions,
+                nsIURI* aBaseURL);
+};
+
+// A single module script. May be used to satisfy multiple load requests.
+
+class ModuleScript final : public LoadedScript
+{
   JS::Heap<JSObject*> mModuleRecord;
   JS::Heap<JS::Value> mParseError;
   JS::Heap<JS::Value> mErrorToRethrow;
@@ -31,8 +70,9 @@ class ModuleScript final : public nsISupports
   ~ModuleScript();
 
 public:
-  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
-  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(ModuleScript)
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(ModuleScript,
+                                                         LoadedScript)
 
   ModuleScript(ScriptLoader* aLoader, ScriptFetchOptions* aFetchOptions,
                nsIURI* aBaseURL);
@@ -41,10 +81,7 @@ public:
   void SetParseError(const JS::Value& aError);
   void SetErrorToRethrow(const JS::Value& aError);
 
-  ScriptLoader* Loader() const { return mLoader; }
-  ScriptFetchOptions* FetchOptions() const { return mFetchOptions; }
   JSObject* ModuleRecord() const { return mModuleRecord; }
-  nsIURI* BaseURL() const { return mBaseURL; }
 
   JS::Value ParseError() const { return mParseError; }
   JS::Value ErrorToRethrow() const { return mErrorToRethrow; }
@@ -56,6 +93,16 @@ public:
   friend void HostFinalizeTopLevelScript(JSFreeOp*, const JS::Value&);
 };
 
+ClassicScript* LoadedScript::AsClassicScript() {
+  MOZ_ASSERT(!IsModuleScript());
+  return static_cast<ClassicScript*>(this);
+}
+
+ModuleScript* LoadedScript::AsModuleScript() {
+  MOZ_ASSERT(IsModuleScript());
+  return static_cast<ModuleScript*>(this);
+}
+
 } // dom namespace
 } // mozilla namespace