--- a/layout/style/test/test_keyframes_vendor_prefix.html
+++ b/layout/style/test/test_keyframes_vendor_prefix.html
@@ -67,59 +67,53 @@ var isStylo = false;
 // block.
 try {
   isStylo = SpecialPowers.getBoolPref('layout.css.servo.enabled');
 } catch(e) {
 }
 
 test(function(t) {
   addStyle(t,
-    { 'dummy': '', // XXX bug 1336863 hackaround: a single insertRule is broken
-                   // on stylo.
-      '@-webkit-keyframes anim': 'from,to { color: rgb(0, 255, 0); }' });
+    { '@-webkit-keyframes anim': 'from,to { color: rgb(0, 255, 0); }' });
 
   var div = addDiv(t, { style: 'animation: anim 100s' });
 
   assert_equals(getComputedStyle(div).color, 'rgb(0, 255, 0)');
 }, '-webkit- prefix keyframes');
 
 test(function(t) {
   addStyle(t,
-    { 'dummy': '', // XXX bug 1336863 hackaround, as above.
-      '@-moz-keyframes anim': 'from,to { color: rgb(0, 255, 0); }' });
+    { '@-moz-keyframes anim': 'from,to { color: rgb(0, 255, 0); }' });
 
   var div = addDiv(t, { style: 'animation: anim 100s' });
 
   assert_equals(getComputedStyle(div).color, 'rgb(0, 255, 0)');
 }, '-moz- prefix keyframes');
 
 test(function(t) {
   addStyle(t,
-    { 'dummy': '', // XXX bug 1336863 hackaround, as above.
-      '@-WEBKIT-keyframes anim': 'from,to { color: rgb(0, 255, 0); }' });
+    { '@-WEBKIT-keyframes anim': 'from,to { color: rgb(0, 255, 0); }' });
 
   var div = addDiv(t, { style: 'animation: anim 100s' });
 
   assert_equals(getComputedStyle(div).color, 'rgb(0, 255, 0)');
 }, '-WEBKIT- prefix keyframes');
 
 test(function(t) {
   addStyle(t,
-    { 'dummy': '', // XXX bug 1336863 hackaround, as above.
-      '@-MOZ-keyframes anim': 'from,to { color: rgb(0, 255, 0); }' });
+    { '@-MOZ-keyframes anim': 'from,to { color: rgb(0, 255, 0); }' });
 
   var div = addDiv(t, { style: 'animation: anim 100s' });
 
   assert_equals(getComputedStyle(div).color, 'rgb(0, 255, 0)');
 }, '-MOZ- prefix keyframes');
 
 test(function(t) {
   addStyle(t,
-    { 'dummy': '', // XXX bug 1336863 hackaround, as above.
-      '@-webkit-KEYFRAMES anim': 'from,to { color: rgb(0, 255, 0); }' });
+    { '@-webkit-KEYFRAMES anim': 'from,to { color: rgb(0, 255, 0); }' });
 
   var div = addDiv(t, { style: 'animation: anim 100s' });
 
   assert_equals(getComputedStyle(div).color, 'rgb(0, 255, 0)');
 }, '-webkit- prefix KEYFRAMES');
 
 test(function(t) {
   if (!isStylo) {