--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -688,16 +688,17 @@ GK_ATOM(ona2dpstatuschanged, "ona2dpstat
 GK_ATOM(onabort, "onabort")
 GK_ATOM(onmozaccesskeynotfound, "onmozaccesskeynotfound")
 GK_ATOM(onactivate, "onactivate")
 GK_ATOM(onadapteradded, "onadapteradded")
 GK_ATOM(onadapterremoved, "onadapterremoved")
 GK_ATOM(onafterprint, "onafterprint")
 GK_ATOM(onafterscriptexecute, "onafterscriptexecute")
 GK_ATOM(onalerting, "onalerting")
+GK_ATOM(onanimationcancel, "onanimationcancel")
 GK_ATOM(onanimationend, "onanimationend")
 GK_ATOM(onanimationiteration, "onanimationiteration")
 GK_ATOM(onanimationstart, "onanimationstart")
 GK_ATOM(onantennaavailablechange, "onantennaavailablechange")
 GK_ATOM(onAppCommand, "onAppCommand")
 GK_ATOM(onappinstalled, "onappinstalled")
 GK_ATOM(onattributechanged, "onattributechanged")
 GK_ATOM(onattributereadreq, "onattributereadreq")

--- a/dom/events/EventNameList.h
+++ b/dom/events/EventNameList.h
@@ -1003,16 +1003,20 @@ EVENT(animationstart,
 EVENT(animationend,
       eAnimationEnd,
       EventNameType_All,
       eAnimationEventClass)
 EVENT(animationiteration,
       eAnimationIteration,
       EventNameType_All,
       eAnimationEventClass)
+EVENT(animationcancel,
+      eAnimationCancel,
+      EventNameType_All,
+      eAnimationEventClass)
 
 // Webkit-prefixed versions of Transition & Animation events, for web compat:
 EVENT(webkitAnimationEnd,
       eWebkitAnimationEnd,
       EventNameType_All,
       eAnimationEventClass)
 EVENT(webkitAnimationIteration,
       eWebkitAnimationIteration,

--- a/widget/EventMessageList.h
+++ b/widget/EventMessageList.h
@@ -335,16 +335,17 @@ NS_EVENT_MESSAGE(eScrolledAreaChanged)
 // CSS Transition & Animation events:
 NS_EVENT_MESSAGE(eTransitionStart)
 NS_EVENT_MESSAGE(eTransitionRun)
 NS_EVENT_MESSAGE(eTransitionEnd)
 NS_EVENT_MESSAGE(eTransitionCancel)
 NS_EVENT_MESSAGE(eAnimationStart)
 NS_EVENT_MESSAGE(eAnimationEnd)
 NS_EVENT_MESSAGE(eAnimationIteration)
+NS_EVENT_MESSAGE(eAnimationCancel)
 
 // Webkit-prefixed versions of Transition & Animation events, for web compat:
 NS_EVENT_MESSAGE(eWebkitTransitionEnd)
 NS_EVENT_MESSAGE(eWebkitAnimationStart)
 NS_EVENT_MESSAGE(eWebkitAnimationEnd)
 NS_EVENT_MESSAGE(eWebkitAnimationIteration)
 
 NS_EVENT_MESSAGE(eSMILBeginEvent)