--- a/dom/media/MediaDecoder.cpp
+++ b/dom/media/MediaDecoder.cpp
@@ -1378,17 +1378,20 @@ void MediaDecoder::AddSizeOfResources(Re
   }
 }
 
 void
 MediaDecoder::NotifyDataArrivedInternal()
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_DIAGNOSTIC_ASSERT(!IsShutdown());
-  mDataArrivedEvent.Notify();
+  mReader->OwnerThread()->Dispatch(
+    NewRunnableMethod("MediaDecoderReader::NotifyDataArrived",
+                      mReader.get(),
+                      &MediaDecoderReader::NotifyDataArrived));
 }
 
 void
 MediaDecoder::NotifyDataArrived()
 {
   NotifyDataArrivedInternal();
   DownloadProgressed();
 }