diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index c5ed38dc27..b0732ee51f 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -224,6 +224,7 @@
 #include "mozilla/dom/PrimitiveConversions.h"
 #include "mozilla/dom/WindowBinding.h"
 #include "nsITabChild.h"
+#include "mozilla/dom/ModuleScript.h"
 #include "mozilla/dom/MediaQueryList.h"
 #include "mozilla/dom/ScriptSettings.h"
 #include "mozilla/dom/NavigatorBinding.h"
@@ -12937,9 +12938,6 @@ nsGlobalWindow::RunTimeoutHandler(Timeout* aTimeout,
     RefPtr<Function> callback = handler->GetCallback();
 
     if (!callback) {
-      // Evaluate the timeout expression.
-      const nsAString& script = handler->GetHandlerText();
-
       const char* filename = nullptr;
       uint32_t lineNo = 0, dummyColumn = 0;
       handler->GetLocation(&filename, &lineNo, &dummyColumn);
@@ -12950,9 +12948,22 @@ nsGlobalWindow::RunTimeoutHandler(Timeout* aTimeout,
       AutoEntryScript aes(this, reason, true);
       JS::CompileOptions options(aes.cx());
       options.setFileAndLine(filename, lineNo).setVersion(JSVERSION_DEFAULT);
+      options.setNoScriptRval(true);
       JS::Rooted<JSObject*> global(aes.cx(), FastGetGlobalJSObject());
-      nsresult rv =
-        nsJSUtils::EvaluateString(aes.cx(), script, global, options);
+      nsresult rv;
+      {
+         nsJSUtils::ExecutionContext exec(aes.cx(), global);
+         rv = exec.Compile(options, handler->GetHandlerText());
+
+         if (rv == NS_OK) {
+           LoadedScript* initiatingScript = handler->GetInitiatingScript();
+           if (initiatingScript) {
+             initiatingScript->AssociateWithScript(exec.GetScript());
+           }
+
+           rv = exec.ExecScript();
+         }
+      }
       if (rv == NS_SUCCESS_DOM_SCRIPT_EVALUATION_THREW_UNCATCHABLE) {
         abortIntervalHandler = true;
       }
diff --git a/dom/base/nsIScriptTimeoutHandler.h b/dom/base/nsIScriptTimeoutHandler.h
index 9679f70478..b1472ad748 100644
--- a/dom/base/nsIScriptTimeoutHandler.h
+++ b/dom/base/nsIScriptTimeoutHandler.h
@@ -14,6 +14,7 @@
 namespace mozilla {
 namespace dom {
 class Function;
+class LoadedScript;
 } // namespace dom
 } // namespace mozilla
 
@@ -44,6 +45,9 @@ public:
 
   // If we have a Function, get the arguments for passing to it.
   virtual const nsTArray<JS::Value>& GetArgs() = 0;
+
+  // If we have an expression, get the initiating script.
+  virtual mozilla::dom::LoadedScript* GetInitiatingScript() = 0;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(nsIScriptTimeoutHandler,
diff --git a/dom/base/nsJSTimeoutHandler.cpp b/dom/base/nsJSTimeoutHandler.cpp
index a370fe03f7..5c836694ae 100644
--- a/dom/base/nsJSTimeoutHandler.cpp
+++ b/dom/base/nsJSTimeoutHandler.cpp
@@ -10,6 +10,7 @@
 #include "mozilla/Likely.h"
 #include "mozilla/Maybe.h"
 #include "mozilla/dom/FunctionBinding.h"
+#include "mozilla/dom/ModuleScript.h"
 #include "nsAXPCNativeCallContext.h"
 #include "nsCOMPtr.h"
 #include "nsContentUtils.h"
@@ -44,6 +45,7 @@ public:
                            nsTArray<JS::Heap<JS::Value>>&& aArguments,
                            ErrorResult& aError);
   nsJSScriptTimeoutHandler(JSContext* aCx, nsGlobalWindow* aWindow,
+                           LoadedScript* aInitiatingScript,
                            const nsAString& aExpression, bool* aAllowEval,
                            ErrorResult& aError);
   nsJSScriptTimeoutHandler(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
@@ -77,6 +79,10 @@ public:
     *aColumn = mColumn;
   }
 
+  virtual LoadedScript* GetInitiatingScript() override {
+    return mInitiatingScript;
+  }
+
   virtual void MarkForCC() override
   {
     if (mFunction) {
@@ -104,6 +110,9 @@ private:
   // it should be used, else use mExpr.
   nsString mExpr;
   RefPtr<Function> mFunction;
+
+  // Initiating script for use when evaluating mExpr on the main thread.
+  RefPtr<LoadedScript> mInitiatingScript;
 };
 
 
@@ -112,6 +121,8 @@ private:
 NS_IMPL_CYCLE_COLLECTION_CLASS(nsJSScriptTimeoutHandler)
 
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsJSScriptTimeoutHandler)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mFunction)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mInitiatingScript)
   tmp->ReleaseJSObjects();
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(nsJSScriptTimeoutHandler)
@@ -151,6 +162,9 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(nsJSScriptTimeoutHandler)
   if (tmp->mFunction) {
     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFunction)
   }
+  if (tmp->mInitiatingScript) {
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mInitiatingScript)
+  }
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(nsJSScriptTimeoutHandler)
@@ -243,12 +257,14 @@ nsJSScriptTimeoutHandler::nsJSScriptTimeoutHandler(JSContext* aCx,
 
 nsJSScriptTimeoutHandler::nsJSScriptTimeoutHandler(JSContext* aCx,
                                                    nsGlobalWindow *aWindow,
+                                                   LoadedScript* aInitiatingScript,
                                                    const nsAString& aExpression,
                                                    bool* aAllowEval,
                                                    ErrorResult& aError)
   : mLineNo(0)
   , mColumn(0)
   , mExpr(aExpression)
+  , mInitiatingScript(aInitiatingScript)
 {
   if (!aWindow->GetContextInternal() || !aWindow->FastGetGlobalJSObject()) {
     // This window was already closed, or never properly initialized,
@@ -352,9 +368,11 @@ already_AddRefed<nsIScriptTimeoutHandler>
 NS_CreateJSTimeoutHandler(JSContext* aCx, nsGlobalWindow *aWindow,
                           const nsAString& aExpression, ErrorResult& aError)
 {
+  LoadedScript* script = ScriptLoader::GetActiveScript(aCx);
+
   bool allowEval = false;
   RefPtr<nsJSScriptTimeoutHandler> handler =
-    new nsJSScriptTimeoutHandler(aCx, aWindow, aExpression, &allowEval, aError);
+    new nsJSScriptTimeoutHandler(aCx, aWindow, script, aExpression, &allowEval, aError);
   if (aError.Failed() || !allowEval) {
     return nullptr;
   }
diff --git a/dom/base/nsJSUtils.cpp b/dom/base/nsJSUtils.cpp
index 467a5b0b53..b43f94422d 100644
--- a/dom/base/nsJSUtils.cpp
+++ b/dom/base/nsJSUtils.cpp
@@ -142,6 +142,7 @@ nsJSUtils::ExecutionContext::ExecutionContext(JSContext* aCx,
   , mRv(NS_OK)
   , mSkip(false)
   , mCoerceToString(false)
+  , mEncodeBytecode(false)
 #ifdef DEBUG
   , mWantsReturnValue(false)
   , mExpectScopeChain(false)
@@ -150,7 +151,6 @@ nsJSUtils::ExecutionContext::ExecutionContext(JSContext* aCx,
 {
   MOZ_ASSERT(aCx == nsContentUtils::GetCurrentJSContext());
   MOZ_ASSERT(NS_IsMainThread());
-  MOZ_ASSERT(nsContentUtils::IsInMicroTask());
   MOZ_ASSERT(mRetValue.isUndefined());
 
   MOZ_ASSERT(js::GetGlobalForObjectCrossCompartment(aGlobal) == aGlobal);
@@ -207,7 +207,7 @@ nsJSUtils::ExecutionContext::JoinCompile(void** aOffThreadToken)
     return mRv;
   }
 
-  if (!StartIncrementalEncoding(mCx, mScript)) {
+  if (mEncodeBytecode && !StartIncrementalEncoding(mCx, mScript)) {
     mSkip = true;
     mRv = EvaluationExceptionToNSResult(mCx);
     return mRv;
@@ -246,7 +246,7 @@ nsJSUtils::ExecutionContext::Compile(JS::CompileOptions& aCompileOptions,
     return mRv;
   }
  
-  if (!StartIncrementalEncoding(mCx, mScript)) {
+  if (mEncodeBytecode && !StartIncrementalEncoding(mCx, mScript)) {
     mSkip = true;
     mRv = EvaluationExceptionToNSResult(mCx);
     return mRv;
@@ -340,6 +340,19 @@ nsresult nsJSUtils::ExecutionContext::ExecScript() {
   return NS_OK;
 }
 
+static bool IsPromiseValue(JSContext* aCx, JS::Handle<JS::Value> aValue) {
+  if (!aValue.isObject()) {
+    return false;
+  }
+
+  JS::Rooted<JSObject*> obj(aCx, js::CheckedUnwrap(&aValue.toObject()));
+  if (!obj) {
+    return false;
+  }
+
+  return JS::IsPromiseObject(obj);
+}
+
 nsresult
 nsJSUtils::ExecutionContext::ExecScript(JS::MutableHandle<JS::Value> aRetValue)
 {
@@ -359,6 +372,15 @@ nsJSUtils::ExecutionContext::ExecScript(JS::MutableHandle<JS::Value> aRetValue)
 #ifdef DEBUG
   mWantsReturnValue = false;
 #endif
+  if (mCoerceToString && IsPromiseValue(mCx, aRetValue)) {
+    // We're a javascript: url and we should treat Promise return values as
+    // undefined.
+    //
+    // Once bug 1477821 is fixed this code might be able to go away, or will
+    // become enshrined in the spec, depending.
+    aRetValue.setUndefined();
+  }
+
   if (mCoerceToString && !aRetValue.isUndefined()) {
     JSString* str = JS::ToString(mCx, aRetValue);
     if (!str) {
diff --git a/dom/base/nsJSUtils.h b/dom/base/nsJSUtils.h
index b1b2b601a6..8d5ccc95ef 100644
--- a/dom/base/nsJSUtils.h
+++ b/dom/base/nsJSUtils.h
@@ -90,6 +90,9 @@ public:
     // Should the result be serialized before being returned.
     bool mCoerceToString;
 
+    // Encode the bytecode before it is being executed.
+    bool mEncodeBytecode;
+
 #ifdef DEBUG
     // Should we set the return value.
     bool mWantsReturnValue;
diff --git a/dom/jsurl/nsJSProtocolHandler.cpp b/dom/jsurl/nsJSProtocolHandler.cpp
index 5db4d69e0d..fe3c12b76a 100644
--- a/dom/jsurl/nsJSProtocolHandler.cpp
+++ b/dom/jsurl/nsJSProtocolHandler.cpp
@@ -275,10 +275,14 @@ nsresult nsJSThunk::EvaluateScript(nsIChannel *aChannel,
     JS::CompileOptions options(cx);
     options.setFileAndLine(mURL.get(), 1)
            .setVersion(JSVERSION_DEFAULT);
-    nsJSUtils::EvaluateOptions evalOptions(cx);
-    evalOptions.setCoerceToString(true);
-    rv = nsJSUtils::EvaluateString(cx, NS_ConvertUTF8toUTF16(script),
-                                   globalJSObject, options, evalOptions, &v);
+    {
+        nsJSUtils::ExecutionContext exec(cx, globalJSObject);
+        exec.SetCoerceToString(true);
+        exec.Compile(options, NS_ConvertUTF8toUTF16(script));
+        rv = exec.ExecScript(&v);
+    }
+
+    js::AssertSameCompartment(cx, v);
 
     if (NS_FAILED(rv) || !(v.isString() || v.isUndefined())) {
         return NS_ERROR_MALFORMED_URI;
diff --git a/dom/plugins/base/nsNPAPIPlugin.cpp b/dom/plugins/base/nsNPAPIPlugin.cpp
index da4f09914f..4b02440e20 100644
--- a/dom/plugins/base/nsNPAPIPlugin.cpp
+++ b/dom/plugins/base/nsNPAPIPlugin.cpp
@@ -1388,14 +1388,23 @@ _evaluate(NPP npp, NPObject* npobj, NPString *script, NPVariant *result)
   options.setFileAndLine(spec, 0)
          .setVersion(JSVERSION_DEFAULT);
   JS::Rooted<JS::Value> rval(cx);
-  nsJSUtils::EvaluateOptions evalOptions(cx);
+  JS::AutoObjectVector scopeChain(cx);
   if (obj != js::GetGlobalForObjectCrossCompartment(obj) &&
-      !evalOptions.scopeChain.append(obj)) {
+      !scopeChain.append(obj)) {
     return false;
   }
   obj = js::GetGlobalForObjectCrossCompartment(obj);
-  nsresult rv = nsJSUtils::EvaluateString(cx, utf16script, obj, options,
-                                          evalOptions, &rval);
+  nsresult rv = NS_OK;
+  {
+    nsJSUtils::ExecutionContext exec(cx, obj);
+    exec.SetScopeChain(scopeChain);
+    exec.Compile(options, utf16script);
+    rv = exec.ExecScript(&rval);
+  }
+
+  if (!JS_WrapValue(cx, &rval)) {
+    return false;
+  }
 
   return NS_SUCCEEDED(rv) &&
          (!result || JSValToNPVariant(npp, cx, rval, result));
diff --git a/dom/script/ScriptLoader.cpp b/dom/script/ScriptLoader.cpp
index f23584c597..d4f76d18b8 100644
--- a/dom/script/ScriptLoader.cpp
+++ b/dom/script/ScriptLoader.cpp
@@ -1072,7 +1072,7 @@ void ScriptLoader::FinishDynamicImport(JSContext* aCx,
   if (NS_FAILED(aResult)) {
     MOZ_ASSERT(!JS_IsExceptionPending(aCx));
     JS_ReportErrorNumberUC(aCx, js::GetErrorMessage, nullptr,
-                           JSMSG_IMPORT_SCRIPT_NOT_FOUND);
+                           JSMSG_DYNAMIC_IMPORT_FAILED);
   }
 
   JS::Rooted<JS::Value> referencingScript(aCx,
@@ -2374,6 +2374,15 @@ ScriptLoader::EvaluateScript(ScriptLoadRequest* aRequest)
   return rv;
 }
 
+/* static */ LoadedScript* ScriptLoader::GetActiveScript(JSContext* aCx) {
+  JS::Value value = JS::GetScriptedCallerPrivate(aCx);
+  if (value.isUndefined()) {
+    return nullptr;
+  }
+
+  return static_cast<LoadedScript*>(value.toPrivate());
+}
+
 void
 ScriptLoader::ProcessPendingRequestsAsync()
 {
diff --git a/dom/script/ScriptLoader.h b/dom/script/ScriptLoader.h
index 53d5ddb4e0..6cf108e331 100644
--- a/dom/script/ScriptLoader.h
+++ b/dom/script/ScriptLoader.h
@@ -34,6 +34,7 @@ namespace mozilla {
 namespace dom {
 
 class AutoJSAPI;
+class LoadedScript;
 class ModuleLoadRequest;
 class ModuleScript;
 class ScriptLoadRequestList;
@@ -586,6 +587,12 @@ public:
   void FinishDynamicImport(JSContext* aCx, ModuleLoadRequest* aRequest,
                            nsresult aResult);
 
+  /*
+   * Get the currently active script. This is used as the initiating script when
+   * executing timeout handler scripts.
+   */
+  static LoadedScript* GetActiveScript(JSContext* aCx);
+
   nsIDocument* GetDocument() const { return mDocument; }
 
 private:
diff --git a/dom/script/moz.build b/dom/script/moz.build
index 280850ed4a..125e62545f 100644
--- a/dom/script/moz.build
+++ b/dom/script/moz.build
@@ -12,6 +12,7 @@ XPIDL_MODULE = 'dom'
 EXPORTS += ['nsIScriptElement.h']
 
 EXPORTS.mozilla.dom += [
+    'ModuleScript.h',
     'ScriptElement.h',
     'ScriptLoader.h',
     'ScriptSettings.h',
diff --git a/dom/worklet/Worklet.cpp b/dom/worklet/Worklet.cpp
index f6baabd935..5bfdc9c176 100644
--- a/dom/worklet/Worklet.cpp
+++ b/dom/worklet/Worklet.cpp
@@ -202,8 +202,6 @@ public:
     compileOptions.setVersion(JSVERSION_DEFAULT);
     compileOptions.setIsRunOnce(true);
 
-    // We only need the setNoScriptRval bit when compiling off-thread here,
-    // since otherwise nsJSUtils::EvaluateString will set it up for us.
     compileOptions.setNoScriptRval(true);
 
     JS::Rooted<JS::Value> unused(cx);
diff --git a/dom/xbl/nsXBLProtoImplField.cpp b/dom/xbl/nsXBLProtoImplField.cpp
index b7c04c25ae..2ace609cc9 100644
--- a/dom/xbl/nsXBLProtoImplField.cpp
+++ b/dom/xbl/nsXBLProtoImplField.cpp
@@ -434,6 +434,7 @@ nsXBLProtoImplField::InstallField(JS::Handle<JSObject*> aBoundNode,
   JS::CompileOptions options(cx);
   options.setFileAndLine(uriSpec.get(), mLineNumber)
          .setVersion(JSVERSION_LATEST);
+#if 1
   nsJSUtils::EvaluateOptions evalOptions(cx);
   if (!nsJSUtils::GetScopeChainForElement(cx, boundElement,
                                           evalOptions.scopeChain)) {
@@ -442,6 +443,21 @@ nsXBLProtoImplField::InstallField(JS::Handle<JSObject*> aBoundNode,
   rv = nsJSUtils::EvaluateString(cx, nsDependentString(mFieldText,
                                                        mFieldTextLength),
                                  scopeObject, options, evalOptions, &result);
+#endif
+#if 0
+  JS::AutoObjectVector scopeChain(cx);
+  if (!nsJSUtils::GetScopeChainForElement(cx, boundElement, scopeChain)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  rv = NS_OK;
+  {
+    nsJSUtils::ExecutionContext exec(cx, scopeObject);
+    exec.SetScopeChain(scopeChain);
+    exec.Compile(options, nsDependentString(mFieldText, mFieldTextLength));
+    rv = exec.ExecScript(&result);
+  }
+#endif
+
   if (NS_FAILED(rv)) {
     return rv;
   }
diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index d49edeb838..1a5d36e104 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -5220,7 +5220,7 @@ template <class ParseHandler>
 inline typename ParseHandler::Node
 Parser<ParseHandler>::importDeclarationOrImportExpr(YieldHandling yieldHandling)
 {
-    MOZ_ASSERT(anyChars.isCurrentTokenType(TOK_IMPORT));
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_IMPORT));
 
     TokenKind tt;
     if (!tokenStream.peekToken(&tt))
@@ -10480,7 +10480,7 @@ template <typename ParseHandler>
 typename ParseHandler::Node
 Parser<ParseHandler>::importExpr(YieldHandling yieldHandling)
 {
-    MOZ_ASSERT(anyChars.isCurrentTokenType(TOK_IMPORT));
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_IMPORT));
 
     Node importHolder = handler.newPosHolder(pos());
     if (!importHolder)
diff --git a/js/src/js.msg b/js/src/js.msg
index 06915af842..b98e6d860b 100644
--- a/js/src/js.msg
+++ b/js/src/js.msg
@@ -592,7 +592,7 @@ MSG_DEF(JSMSG_MISSING_NAMESPACE_EXPORT,  0, JSEXN_SYNTAXERR, "export not found f
 MSG_DEF(JSMSG_MISSING_EXPORT,            1, JSEXN_SYNTAXERR, "local binding for export '{0}' not found")
 MSG_DEF(JSMSG_BAD_MODULE_STATUS,         0, JSEXN_INTERNALERR, "module record has unexpected status")
 MSG_DEF(JSMSG_NO_DYNAMIC_IMPORT,         0, JSEXN_SYNTAXERR, "dynamic module import is not implemented")
-MSG_DEF(JSMSG_IMPORT_SCRIPT_NOT_FOUND,   0, JSEXN_TYPEERR, "can't find referencing script for dynamic module import")
+MSG_DEF(JSMSG_DYNAMIC_IMPORT_FAILED,     0, JSEXN_TYPEERR, "error loading dynamically imported module")
 MSG_DEF(JSMSG_BAD_MODULE_SPECIFIER,      1, JSEXN_TYPEERR, "error resolving module specifier '{0}'")
 
 // Promise
diff --git a/js/src/jsfriendapi.cpp b/js/src/jsfriendapi.cpp
index aad0756f03..0cd57ab52b 100644
--- a/js/src/jsfriendapi.cpp
+++ b/js/src/jsfriendapi.cpp
@@ -366,6 +366,12 @@ js::AssertSameCompartment(JSContext* cx, JSObject* obj)
     assertSameCompartment(cx, obj);
 }
 
+JS_FRIEND_API(void)
+js::AssertSameCompartment(JSContext* cx, JS::HandleValue v)
+{
+    assertSameCompartment(cx, v);
+}
+
 #ifdef DEBUG
 JS_FRIEND_API(void)
 js::AssertSameCompartment(JSObject* objA, JSObject* objB)
diff --git a/js/src/jsfriendapi.h b/js/src/jsfriendapi.h
index d1c2289634..71c9deb94e 100644
--- a/js/src/jsfriendapi.h
+++ b/js/src/jsfriendapi.h
@@ -659,6 +659,9 @@ GetPrototypeNoProxy(JSObject* obj);
 JS_FRIEND_API(void)
 AssertSameCompartment(JSContext* cx, JSObject* obj);
 
+JS_FRIEND_API(void)
+AssertSameCompartment(JSContext* cx, JS::HandleValue v);
+
 #ifdef JS_DEBUG
 JS_FRIEND_API(void)
 AssertSameCompartment(JSObject* objA, JSObject* objB);
diff --git a/js/src/jsscript.cpp b/js/src/jsscript.cpp
index fce520e5e7..e6308ceb22 100644
--- a/js/src/jsscript.cpp
+++ b/js/src/jsscript.cpp
@@ -1401,7 +1401,7 @@ const Class ScriptSourceObject::class_ = {
 };
 
 ScriptSourceObject*
-ScriptSourceObject::create(ExclusiveContext* cx, ScriptSource* source)
+ScriptSourceObject::createInternal(ExclusiveContext* cx, ScriptSource* source, HandleObject canonical)
 {
     RootedObject object(cx, NewObjectWithGivenProto(cx, &class_, nullptr));
     if (!object)
@@ -1411,6 +1411,12 @@ ScriptSourceObject::create(ExclusiveContext* cx, ScriptSource* source)
     source->incref();    // The matching decref is in ScriptSourceObject::finalize.
     sourceObject->initReservedSlot(SOURCE_SLOT, PrivateValue(source));
 
+    if (canonical) {
+        sourceObject->initReservedSlot(CANONICAL_SLOT, ObjectValue(*canonical));
+    } else {
+        sourceObject->initReservedSlot(CANONICAL_SLOT, ObjectValue(*sourceObject));
+    }
+
     // The remaining slots should eventually be populated by a call to
     // initFromOptions. Poison them until that point.
     sourceObject->initReservedSlot(ELEMENT_SLOT, MagicValue(JS_GENERIC_MAGIC));
@@ -1420,6 +1426,20 @@ ScriptSourceObject::create(ExclusiveContext* cx, ScriptSource* source)
     return sourceObject;
 }
 
+ScriptSourceObject*
+ScriptSourceObject::create(ExclusiveContext* cx, ScriptSource* source)
+{
+    return createInternal(cx, source, nullptr);
+}
+
+ScriptSourceObject* ScriptSourceObject::unwrappedCanonical() const
+{
+    MOZ_ASSERT(CurrentThreadCanAccessRuntime(runtimeFromAnyThread()));
+ 
+    JSObject* obj = &getReservedSlot(CANONICAL_SLOT).toObject();
+    return &UncheckedUnwrap(obj)->as<ScriptSourceObject>();
+}
+
 /* static */ bool
 ScriptSourceObject::initFromOptions(JSContext* cx, HandleScriptSource source,
                                     const ReadOnlyCompileOptions& options)
diff --git a/js/src/jsscript.h b/js/src/jsscript.h
index c9f5a927bb..e2225f0cda 100644
--- a/js/src/jsscript.h
+++ b/js/src/jsscript.h
@@ -637,6 +637,14 @@ class ScriptSourceObject : public NativeObject
 {
     static const ClassOps classOps_;
 
+    static ScriptSourceObject* createInternal(ExclusiveContext* cx, ScriptSource* source,
+                                              HandleObject canonical);
+
+    bool isCanonical() const {
+      return &getReservedSlot(CANONICAL_SLOT).toObject() == this;
+    }
+    ScriptSourceObject* unwrappedCanonical() const;
+
   public:
     static const Class class_;
 
@@ -684,6 +692,7 @@ class ScriptSourceObject : public NativeObject
   private:
     enum {
         SOURCE_SLOT = 0,
+        CANONICAL_SLOT,
         ELEMENT_SLOT,
         ELEMENT_PROPERTY_SLOT,
         INTRODUCTION_SCRIPT_SLOT,
diff --git a/netwerk/dns/mdns/libmdns/MDNSResponderReply.cpp b/netwerk/dns/mdns/libmdns/MDNSResponderReply.cpp
index 7aa5b3759a..124c0251da 100644
--- a/netwerk/dns/mdns/libmdns/MDNSResponderReply.cpp
+++ b/netwerk/dns/mdns/libmdns/MDNSResponderReply.cpp
@@ -6,6 +6,7 @@
 #include "MDNSResponderReply.h"
 #include "mozilla/EndianUtils.h"
 #include "private/pprio.h"
+#include "nsSocketTransportService2.h"
 
 namespace mozilla {
 namespace net {
diff --git a/netwerk/dns/mdns/libmdns/nsDNSServiceDiscovery.cpp b/netwerk/dns/mdns/libmdns/nsDNSServiceDiscovery.cpp
index cec8033d18..9676c64835 100644
--- a/netwerk/dns/mdns/libmdns/nsDNSServiceDiscovery.cpp
+++ b/netwerk/dns/mdns/libmdns/nsDNSServiceDiscovery.cpp
@@ -8,6 +8,7 @@
 #include "nsICancelable.h"
 #include "nsXULAppAPI.h"
 #include "private/pprio.h"
+#include "MainThreadUtils.h"
 
 namespace mozilla {
 namespace net {