--- a/dom/media/gmp/GMPParent.cpp
+++ b/dom/media/gmp/GMPParent.cpp
@@ -930,22 +930,23 @@ RefPtr<GenericPromise>
 GMPParent::ReadChromiumManifestFile(nsIFile* aFile)
 {
   nsAutoCString json;
   if (!ReadIntoString(aFile, json, 5 * 1024)) {
     return GenericPromise::CreateAndReject(NS_ERROR_FAILURE, __func__);
   }
 
   // DOM JSON parsing needs to run on the main thread.
-  return InvokeAsync(AbstractThread::MainThread(), this, __func__,
+  return InvokeAsync<nsString&&>(
+    AbstractThread::MainThread(), this, __func__,
     &GMPParent::ParseChromiumManifest, NS_ConvertUTF8toUTF16(json));
 }
 
 RefPtr<GenericPromise>
-GMPParent::ParseChromiumManifest(nsString aJSON)
+GMPParent::ParseChromiumManifest(const nsAString& aJSON)
 {
   LOGD("%s: for '%s'", __FUNCTION__, NS_LossyConvertUTF16toASCII(aJSON).get());
 
   MOZ_ASSERT(NS_IsMainThread());
   mozilla::dom::WidevineCDMManifest m;
   if (!m.Init(aJSON)) {
     return GenericPromise::CreateAndReject(NS_ERROR_FAILURE, __func__);
   }

--- a/dom/media/gmp/GMPParent.h
+++ b/dom/media/gmp/GMPParent.h
@@ -170,17 +170,17 @@ public:
 
 private:
   ~GMPParent();
 
   RefPtr<GeckoMediaPluginServiceParent> mService;
   bool EnsureProcessLoaded();
   RefPtr<GenericPromise> ReadGMPMetaData();
   RefPtr<GenericPromise> ReadGMPInfoFile(nsIFile* aFile);
-  RefPtr<GenericPromise> ParseChromiumManifest(nsString aJSON); // Main thread.
+  RefPtr<GenericPromise> ParseChromiumManifest(const nsAString& aJSON); // Main thread.
   RefPtr<GenericPromise> ReadChromiumManifestFile(nsIFile* aFile); // GMP thread.
 #ifdef MOZ_CRASHREPORTER
   void WriteExtraDataForMinidump(CrashReporter::AnnotationTable& notes);
   void GetCrashID(nsString& aResult);
 #endif
   void ActorDestroy(ActorDestroyReason aWhy) override;
 
   PCrashReporterParent* AllocPCrashReporterParent(const NativeThreadId& aThread) override;