diff --git a/dom/html/TextTrackManager.cpp b/dom/html/TextTrackManager.cpp
index 9de664084274..b39628dd8dcb 100644
--- a/dom/html/TextTrackManager.cpp
+++ b/dom/html/TextTrackManager.cpp
@@ -145,7 +145,7 @@ TextTrackManager::AddTextTrack(TextTrackKind aKind, const nsAString& aLabel,
   AddCues(ttrack);
 
   if (aTextTrackSource == Track) {
-    HonorUserPreferencesForTrackSelection();
+    NS_DispatchToMainThread(NewRunnableMethod(this, &TextTrackManager::HonorUserPreferencesForTrackSelection));
   }
 
   return ttrack.forget();
@@ -160,7 +160,7 @@ TextTrackManager::AddTextTrack(TextTrack* aTextTrack)
   mTextTracks->AddTextTrack(aTextTrack, CompareTextTracks(mMediaElement));
   AddCues(aTextTrack);
   if (aTextTrack->GetTextTrackSource() == Track) {
-    HonorUserPreferencesForTrackSelection();
+    NS_DispatchToMainThread(NewRunnableMethod(this, &TextTrackManager::HonorUserPreferencesForTrackSelection));
   }
 }
 
diff --git a/testing/web-platform/tests/html/semantics/embedded-content/media-elements/interfaces/TextTrack/cues.html b/testing/web-platform/tests/html/semantics/embedded-content/media-elements/interfaces/TextTrack/cues.html
index 11d33b771165..4b7808c96389 100644
--- a/testing/web-platform/tests/html/semantics/embedded-content/media-elements/interfaces/TextTrack/cues.html
+++ b/testing/web-platform/tests/html/semantics/embedded-content/media-elements/interfaces/TextTrack/cues.html
@@ -79,7 +79,7 @@ async_test(function(){
     var video = document.createElement('video');
     var t1 = video.addTextTrack('subtitles');
     var t1_cues = t1.cues;
-    t1.mode = 'showing';
+    t1.mode = 'hidden';
     var track = document.createElement('track');
     track['default'] = true;
     video.appendChild(track); // queues a task to "honor user preferences...", media element event task source