--- a/dom/media/mediasource/test/mediasource.js
+++ b/dom/media/mediasource/test/mediasource.js
@@ -50,17 +50,17 @@ function range(start, end) {
     rv.push(i);
   }
   return rv;
 }
 
 function once(target, name, cb) {
   var p = new Promise(function(resolve, reject) {
     target.addEventListener(name, function() {
-      target.removeEventListener(name, cb);
+      target.removeEventListener(name, arguments.callee);
       resolve();
     });
   });
   if (cb) {
     p.then(cb);
   }
   return p;
 }