--- a/dom/media/platforms/wmf/WMFVideoMFTManager.cpp
+++ b/dom/media/platforms/wmf/WMFVideoMFTManager.cpp
@@ -459,18 +459,18 @@ WMFVideoMFTManager::InitializeDXVA(bool 
                                           : backend,
                                mKnowsCompositor,
                                mDXVAFailureReason);
 
   if (NS_IsMainThread()) {
     event->Run();
   } else {
     // This logic needs to run on the main thread
-    nsCOMPtr<nsIThread> mainThread = do_GetMainThread();
-    mozilla::SyncRunnable::DispatchToThread(mainThread, event);
+    mozilla::SyncRunnable::DispatchToThread(
+      SystemGroup::EventTargetFor(mozilla::TaskCategory::Other), event);
   }
   mDXVA2Manager = event->mDXVA2Manager;
 
   return mDXVA2Manager != nullptr;
 }
 
 bool
 WMFVideoMFTManager::ValidateVideoInfo()
@@ -709,18 +709,18 @@ WMFVideoMFTManager::CanUseDXVA(IMFMediaT
   // a crash guard protecting it.
   RefPtr<SupportsConfigEvent> event =
     new SupportsConfigEvent(mDXVA2Manager, aType, framerate);
 
   if (NS_IsMainThread()) {
     event->Run();
   } else {
     // This logic needs to run on the main thread
-    nsCOMPtr<nsIThread> mainThread = do_GetMainThread();
-    mozilla::SyncRunnable::DispatchToThread(mainThread, event);
+    mozilla::SyncRunnable::DispatchToThread(
+      SystemGroup::EventTargetFor(mozilla::TaskCategory::Other), event);
   }
 
   return event->mSupportsConfig;
 }
 
 HRESULT
 WMFVideoMFTManager::ConfigureVideoFrameGeometry()
 {