--- a/dom/base/WebSocket.cpp
+++ b/dom/base/WebSocket.cpp
@@ -2628,19 +2628,26 @@ public:
     : MainThreadWorkerRunnable(aWorkerPrivate)
     , mImpl(aImpl)
   {
   }
 
   bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override
   {
     aWorkerPrivate->AssertIsOnWorkerThread();
+    aWorkerPrivate->ModifyBusyCountFromWorker(true);
     return !NS_FAILED(mImpl->CancelInternal());
   }
 
+  void PostRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+               bool aRunResult) override
+  {
+    aWorkerPrivate->ModifyBusyCountFromWorker(false);
+  }
+
 private:
   RefPtr<WebSocketImpl> mImpl;
 };
 
 } // namespace
 
 // Window closed, stop/reload button pressed, user navigated away from page, etc.
 NS_IMETHODIMP
@@ -2770,29 +2777,31 @@ public:
     , mWebSocketImpl(aImpl)
     , mEvent(Move(aEvent))
   {
   }
 
   bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override
   {
     aWorkerPrivate->AssertIsOnWorkerThread();
+    aWorkerPrivate->ModifyBusyCountFromWorker(true);
 
     // No messages when disconnected.
     if (mWebSocketImpl->mDisconnectingOrDisconnected) {
       NS_WARNING("Dispatching a WebSocket event after the disconnection!");
       return true;
     }
 
     return !NS_FAILED(mEvent->Run());
   }
 
   void PostRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
                bool aRunResult) override
   {
+    aWorkerPrivate->ModifyBusyCountFromWorker(false);
   }
 
   bool
   PreDispatch(WorkerPrivate* aWorkerPrivate) override
   {
     // We don't call WorkerRunnable::PreDispatch because it would assert the
     // wrong thing about which thread we're on.  We're on whichever thread the
     // channel implementation is running on (probably the main thread or socket