--- a/dom/media/MediaRecorder.cpp
+++ b/dom/media/MediaRecorder.cpp
@@ -811,19 +811,20 @@ private:
     // end the session.
     mNeedSessionEndTask = false;
   }
   // application should get blob and onstop event
   void DoSessionEndTask(nsresult rv)
   {
     MOZ_ASSERT(NS_IsMainThread());
     CleanupStreams();
-
-    NS_DispatchToMainThread(
-      new DispatchStartEventRunnable(this, NS_LITERAL_STRING("start")));
+    if (!mIsStartEventFired) {
+      NS_DispatchToMainThread(
+        new DispatchStartEventRunnable(this, NS_LITERAL_STRING("start")));
+    }
 
     if (NS_FAILED(rv)) {
       mRecorder->ForceInactive();
       NS_DispatchToMainThread(
         NewRunnableMethod<nsresult>("dom::MediaRecorder::NotifyError",
                                     mRecorder,
                                     &MediaRecorder::NotifyError,
                                     rv));