--- a/dom/media/test/eme.js
+++ b/dom/media/test/eme.js
@@ -450,16 +450,17 @@ function SetupEME(test, token, params)
   });
   return v;
 }
 
 function SetupEMEPref(callback) {
   var prefs = [
     [ "media.mediasource.enabled", true ],
     [ "media.mediasource.webm.enabled", true ],
+    [ "media.eme.vp9-in-mp4.enabled", true ],
   ];
 
   if (SpecialPowers.Services.appinfo.name == "B2G" ||
       !manifestVideo().canPlayType("video/mp4")) {
     // XXX remove once we have mp4 PlatformDecoderModules on all platforms.
     prefs.push([ "media.use-blank-decoder", true ]);
   }