--- a/dom/media/mediasource/test/mediasource.js
+++ b/dom/media/mediasource/test/mediasource.js
@@ -48,18 +48,18 @@ function range(start, end) {
   for (var i = start; i < end; ++i) {
     rv.push(i);
   }
   return rv;
 }
 
 function once(target, name, cb) {
   var p = new Promise(function(resolve, reject) {
-    target.addEventListener(name, function() {
-      target.removeEventListener(name, arguments.callee);
+    target.addEventListener(name, function onceEvent() {
+      target.removeEventListener(name, onceEvent);
       resolve();
     });
   });
   if (cb) {
     p.then(cb);
   }
   return p;
 }

--- a/dom/media/test/manifest.js
+++ b/dom/media/test/manifest.js
@@ -1349,18 +1349,18 @@ function removeNodeAndSource(n) {
   n.src = "";
   while (n.firstChild) {
     n.removeChild(n.firstChild);
   }
 }
 
 function once(target, name, cb) {
   var p = new Promise(function(resolve, reject) {
-    target.addEventListener(name, function() {
-      target.removeEventListener(name, arguments.callee);
+    target.addEventListener(name, function onceEvent() {
+      target.removeEventListener(name, onceEvent);
       resolve();
     });
   });
   if (cb) {
     p.then(cb);
   }
   return p;
 }