--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -947,16 +947,20 @@ GK_ATOM(onupgradeneeded, "onupgradeneede
 GK_ATOM(onussdreceived, "onussdreceived")
 GK_ATOM(onversionchange, "onversionchange")
 GK_ATOM(onvoicechange, "onvoicechange")
 GK_ATOM(onvoiceschanged, "onvoiceschanged")
 GK_ATOM(onwebkitAnimationEnd, "onwebkitAnimationEnd")
 GK_ATOM(onwebkitAnimationIteration, "onwebkitAnimationIteration")
 GK_ATOM(onwebkitAnimationStart, "onwebkitAnimationStart")
 GK_ATOM(onwebkitTransitionEnd, "onwebkitTransitionEnd")
+GK_ATOM(onwebkitanimationend, "onwebkitanimationend")
+GK_ATOM(onwebkitanimationiteration, "onwebkitanimationiteration")
+GK_ATOM(onwebkitanimationstart, "onwebkitanimationstart")
+GK_ATOM(onwebkittransitionend, "onwebkittransitionend")
 GK_ATOM(onwebsocket, "onwebsocket")
 GK_ATOM(onwheel, "onwheel")
 GK_ATOM(open, "open")
 GK_ATOM(optgroup, "optgroup")
 GK_ATOM(optimum, "optimum")
 GK_ATOM(option, "option")
 GK_ATOM(_or, "or")
 GK_ATOM(order, "order")

--- a/dom/events/EventNameList.h
+++ b/dom/events/EventNameList.h
@@ -969,32 +969,50 @@ EVENT(animationend,
       EventNameType_All,
       eAnimationEventClass)
 EVENT(animationiteration,
       eAnimationIteration,
       EventNameType_All,
       eAnimationEventClass)
 
 // Webkit-prefixed versions of Transition & Animation events, for web compat:
-NON_IDL_EVENT(webkitTransitionEnd,
-              eWebkitTransitionEnd,
-              EventNameType_None,
-              eTransitionEventClass)
-NON_IDL_EVENT(webkitAnimationEnd,
-              eWebkitAnimationEnd,
-              EventNameType_None,
-              eAnimationEventClass)
-NON_IDL_EVENT(webkitAnimationIteration,
-              eWebkitAnimationIteration,
-              EventNameType_None,
-              eAnimationEventClass)
-NON_IDL_EVENT(webkitAnimationStart,
-              eWebkitAnimationStart,
-              EventNameType_None,
-              eAnimationEventClass)
+EVENT(webkitAnimationEnd,
+      eWebkitAnimationEnd,
+      EventNameType_All,
+      eAnimationEventClass)
+EVENT(webkitAnimationIteration,
+      eWebkitAnimationIteration,
+      EventNameType_All,
+      eAnimationEventClass)
+EVENT(webkitAnimationStart,
+      eWebkitAnimationStart,
+      EventNameType_All,
+      eAnimationEventClass)
+EVENT(webkitTransitionEnd,
+      eWebkitTransitionEnd,
+      EventNameType_All,
+      eTransitionEventClass)
+#ifndef MESSAGE_TO_EVENT
+EVENT(webkitanimationend,
+      eWebkitAnimationEnd,
+      EventNameType_All,
+      eAnimationEventClass)
+EVENT(webkitanimationiteration,
+      eWebkitAnimationIteration,
+      EventNameType_All,
+      eAnimationEventClass)
+EVENT(webkitanimationstart,
+      eWebkitAnimationStart,
+      EventNameType_All,
+      eAnimationEventClass)
+EVENT(webkittransitionend,
+      eWebkitTransitionEnd,
+      EventNameType_All,
+      eTransitionEventClass)
+#endif
 
 NON_IDL_EVENT(audioprocess,
               eAudioProcess,
               EventNameType_None,
               eBasicEventClass)
 
 NON_IDL_EVENT(complete,
               eAudioComplete,

--- a/dom/webidl/EventHandler.webidl
+++ b/dom/webidl/EventHandler.webidl
@@ -126,16 +126,23 @@ interface GlobalEventHandlers {
            [Pref="pointer-lock-api.prefixed.enabled"]
            attribute EventHandler onmozpointerlockerror;
 
            // CSS-Animation and CSS-Transition handlers.
            attribute EventHandler onanimationend;
            attribute EventHandler onanimationiteration;
            attribute EventHandler onanimationstart;
            attribute EventHandler ontransitionend;
+
+           // CSS-Animation and CSS-Transition legacy handlers.
+           // This handler isn't standard.
+           attribute EventHandler onwebkitanimationend;
+           attribute EventHandler onwebkitanimationiteration;
+           attribute EventHandler onwebkitanimationstart;
+           attribute EventHandler onwebkittransitionend;
 };
 
 [NoInterfaceObject]
 interface WindowEventHandlers {
            attribute EventHandler onafterprint;
            attribute EventHandler onbeforeprint;
            attribute OnBeforeUnloadEventHandler onbeforeunload;
            attribute EventHandler onhashchange;

--- a/layout/style/test/test_animations_event_handler_attribute.html
+++ b/layout/style/test/test_animations_event_handler_attribute.html
@@ -49,23 +49,22 @@ function handleEvent(event) {
   if (event.target.receivedEventType) {
     ok(false, `Received ${event.type} event, but this element have previous `
               `received event '${event.target.receivedEventType}'.`);
     return;
   }
   event.target.receivedEventType = event.type;
 }
 
-function checkReceivedEvents(eventType, elements, evalFunc) {
-  if (!evalFunc) { evalFunc = is; }
+function checkReceivedEvents(eventType, elements) {
   elements.forEach(element => {
-    evalFunc(element.receivedEventType, eventType,
-             `Expected to receive '${eventType}', got
-              '${element.receivedEventType}', for event handler registered
-              using ${element.handlerType}`);
+    is(element.receivedEventType, eventType,
+       `Expected to receive '${eventType}', got
+        '${element.receivedEventType}', for event handler registered
+        using ${element.handlerType}`);
     element.receivedEventType = undefined;
   });
 }
 
 // Take over the refresh driver right from the start.
 advance_clock(0);
 
 // 1. Test CSS Animation event handlers.
@@ -111,39 +110,39 @@ var targets = createAndRegisterTargets([
                                          'onwebkitanimationiteration',
                                          'onwebkitanimationend' ]);
 targets.forEach(div => {
   div.setAttribute('style', 'animation: anim 100ms 2');
   getComputedStyle(div).animationName;  // flush
 });
 
 advance_clock(0);
-checkReceivedEvents("webkitAnimationStart", targets, todo_is);
+checkReceivedEvents("webkitAnimationStart", targets);
 
 advance_clock(100);
-checkReceivedEvents("webkitAnimationIteration", targets, todo_is);
+checkReceivedEvents("webkitAnimationIteration", targets);
 
 advance_clock(200);
-checkReceivedEvents("webkitAnimationEnd", targets, todo_is);
+checkReceivedEvents("webkitAnimationEnd", targets);
 
 targets.forEach(div => { div.remove(); });
 
 // 4. Test prefixed CSS Transition event handlers.
 
 advance_clock(0);
 var targets = createAndRegisterTargets([ 'onwebkittransitionend' ]);
 targets.forEach(div => {
   div.style.transition = 'margin-left 100ms';
   getComputedStyle(div).marginLeft; // flush
   div.style.marginLeft = "200px";
   getComputedStyle(div).marginLeft; // flush
 });
 
 advance_clock(100);
-checkReceivedEvents("webkitTransitionEnd", targets, todo_is);
+checkReceivedEvents("webkitTransitionEnd", targets);
 
 targets.forEach(div => { div.remove(); });
 
 SpecialPowers.DOMWindowUtils.restoreNormalRefresh();
 
 </script>
 </body>
 </html>