--- a/dom/media/test/background_video.js
+++ b/dom/media/test/background_video.js
@@ -46,17 +46,17 @@ function waitUntilPlaying(video) {
 /**
  * @param {HTMLMediaElement} video Video element under test.
  * @returns {Promise} Promise which is resolved when video 'ended' event fires.
  */
 function waitUntilEnded(video) {
   Log(video.token, "Waiting for ended");
   if (video.ended) {
     ok(true, video.token + " already ended");
-    return Promise.success();
+    return Promise.resolve();
   }
 
   return once(video, 'ended', () => { ok(true, video.token + " ended"); });
 }
 
 /**
  * @param {HTMLMediaElement} video Video element under test.
  * @returns {Promise} Promise that is resolved when video decode suspends.