--- a/dom/media/MediaStreamGraphImpl.h
+++ b/dom/media/MediaStreamGraphImpl.h
@@ -738,16 +738,19 @@ public:
     // to shut down the graph thread(s).
     LIFECYCLE_WAITING_FOR_THREAD_SHUTDOWN,
     // Graph threads have shut down but we're waiting for remaining streams
     // to be destroyed. Only happens during application shutdown and on
     // completed non-realtime graphs, since normally we'd only shut down a
     // realtime graph when it has no streams.
     LIFECYCLE_WAITING_FOR_STREAM_DESTRUCTION
   };
+  /**
+   * Modified only on the main thread in mMonitor.
+   */
   LifecycleState mLifecycleState;
   /**
    * The graph should stop processing at or after this time.
    */
   GraphTime mEndTime;
 
   /**
    * True when we need to do a forced shutdown during application shutdown.