diff --git a/dom/media/MediaDecoderStateMachine.cpp b/dom/media/MediaDecoderStateMachine.cpp
index a034ae78ec64..6e752c01e897 100644
--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -2491,9 +2491,10 @@ MediaDecoderStateMachine::ShutdownReader()
 }
 
 void
-MediaDecoderStateMachine::FinishShutdown()
+MediaDecoderStateMachine::FinishShutdown(bool aSuccess)
 {
   MOZ_ASSERT(OnStateMachineThread());
+  MOZ_ASSERT(aSuccess);
   ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
 
   // The reader's listeners hold references to the state machine,
diff --git a/dom/media/MediaDecoderStateMachine.h b/dom/media/MediaDecoderStateMachine.h
index 1592ab8266ae..32ca577cdc45 100644
--- a/dom/media/MediaDecoderStateMachine.h
+++ b/dom/media/MediaDecoderStateMachine.h
@@ -163,7 +163,7 @@ public:
   void SetDormant(bool aDormant);
   void Shutdown();
   void ShutdownReader();
-  void FinishShutdown();
+  void FinishShutdown(bool aSuccess);
 
   // Called from the main thread to get the duration. The decoder monitor
   // must be obtained before calling this. It is in units of microseconds.
diff --git a/dom/media/MediaPromise.h b/dom/media/MediaPromise.h
index 02934d6dd20e..8578c97190ac 100644
--- a/dom/media/MediaPromise.h
+++ b/dom/media/MediaPromise.h
@@ -155,23 +155,6 @@ protected:
     const char* mCallSite;
   };
 
-  /*
-   * We create two specializations for invoking Resolve/Reject Methods so as to
-   * make the resolve/reject value argument "optional" via SFINAE.
-   */
-
-  template<typename ThisType, typename ValueType>
-  static void InvokeCallbackMethod(ThisType* aThisVal, void(ThisType::*aMethod)(ValueType), ValueType aValue)
-  {
-      ((*aThisVal).*aMethod)(aValue);
-  }
-
-  template<typename ThisType, typename ValueType>
-  static void InvokeCallbackMethod(ThisType* aThisVal, void(ThisType::*aMethod)(), ValueType aValue)
-  {
-      ((*aThisVal).*aMethod)();
-  }
-
   template<typename TargetType, typename ThisType,
            typename ResolveMethodType, typename RejectMethodType>
   class ThenValue : public ThenValueBase
@@ -204,12 +187,12 @@ protected:
   protected:
     virtual void DoResolve(ResolveValueType aResolveValue)
     {
-      InvokeCallbackMethod(mThisVal.get(), mResolveMethod, aResolveValue);
+      ((*mThisVal).*mResolveMethod)(aResolveValue);
     }
 
     virtual void DoReject(RejectValueType aRejectValue)
     {
-      InvokeCallbackMethod(mThisVal.get(), mRejectMethod, aRejectValue);
+      ((*mThisVal).*mRejectMethod)(aRejectValue);
     }
 
     virtual ~ThenValue() {}
diff --git a/dom/media/mediasource/MediaSourceReader.cpp b/dom/media/mediasource/MediaSourceReader.cpp
index f52dbdf1afec..c4ae0cc40455 100644
--- a/dom/media/mediasource/MediaSourceReader.cpp
+++ b/dom/media/mediasource/MediaSourceReader.cpp
@@ -299,13 +299,14 @@ MediaSourceReader::Shutdown()
   MOZ_ASSERT(mMediaSourceShutdownPromise.IsEmpty());
   nsRefPtr<ShutdownPromise> p = mMediaSourceShutdownPromise.Ensure(__func__);
 
-  ContinueShutdown();
+  ContinueShutdown(true);
   return p;
 }
 
 void
-MediaSourceReader::ContinueShutdown()
+MediaSourceReader::ContinueShutdown(bool aSuccess)
 {
+  MOZ_ASSERT(aSuccess);
   if (mTrackBuffers.Length()) {
     mTrackBuffers[0]->Shutdown()->Then(GetTaskQueue(), __func__, this,
                                        &MediaSourceReader::ContinueShutdown,
diff --git a/dom/media/mediasource/MediaSourceReader.h b/dom/media/mediasource/MediaSourceReader.h
index cf0eb6e02bd2..f9020d1f6246 100644
--- a/dom/media/mediasource/MediaSourceReader.h
+++ b/dom/media/mediasource/MediaSourceReader.h
@@ -180,7 +180,7 @@ private:
 
   bool mHasEssentialTrackBuffers;
 
-  void ContinueShutdown();
+  void ContinueShutdown(bool aSuccess);
   MediaPromiseHolder<ShutdownPromise> mMediaSourceShutdownPromise;
 #ifdef MOZ_FMP4
   nsRefPtr<SharedDecoderManager> mSharedDecoderManager;
diff --git a/dom/media/mediasource/TrackBuffer.cpp b/dom/media/mediasource/TrackBuffer.cpp
index 793da5a2e2de..d16c0b059a90 100644
--- a/dom/media/mediasource/TrackBuffer.cpp
+++ b/dom/media/mediasource/TrackBuffer.cpp
@@ -112,8 +112,9 @@ TrackBuffer::Shutdown()
 }
 
 void
-TrackBuffer::ContinueShutdown()
+TrackBuffer::ContinueShutdown(bool aSuccess)
 {
+  MOZ_ASSERT(aSuccess);
   ReentrantMonitorAutoEnter mon(mParentDecoder->GetReentrantMonitor());
   if (mDecoders.Length()) {
     mDecoders[0]->GetReader()->Shutdown()
diff --git a/dom/media/mediasource/TrackBuffer.h b/dom/media/mediasource/TrackBuffer.h
index 79e2930ece68..ef2ee18dd942 100644
--- a/dom/media/mediasource/TrackBuffer.h
+++ b/dom/media/mediasource/TrackBuffer.h
@@ -160,7 +160,7 @@ private:
   // Protected by mParentDecoder's monitor.
   MediaInfo mInfo;
 
-  void ContinueShutdown();
+  void ContinueShutdown(bool aSuccess);
   MediaPromiseHolder<ShutdownPromise> mShutdownPromise;
 };