--- a/dom/events/AnimationEvent.cpp
+++ b/dom/events/AnimationEvent.cpp
@@ -44,17 +44,17 @@ AnimationEvent::Constructor(const Global
   RefPtr<AnimationEvent> e = new AnimationEvent(t, nullptr, nullptr);
   bool trusted = e->Init(t);
 
   e->InitEvent(aType, aParam.mBubbles, aParam.mCancelable);
 
   InternalAnimationEvent* internalEvent = e->mEvent->AsAnimationEvent();
   internalEvent->mAnimationName = aParam.mAnimationName;
   internalEvent->mElapsedTime = aParam.mElapsedTime;
-  internalEvent->pseudoElement = aParam.mPseudoElement;
+  internalEvent->mPseudoElement = aParam.mPseudoElement;
 
   e->SetTrusted(trusted);
   return e.forget();
 }
 
 NS_IMETHODIMP
 AnimationEvent::GetAnimationName(nsAString& aAnimationName)
 {
@@ -73,17 +73,17 @@ float
 AnimationEvent::ElapsedTime()
 {
   return mEvent->AsAnimationEvent()->mElapsedTime;
 }
 
 NS_IMETHODIMP
 AnimationEvent::GetPseudoElement(nsAString& aPseudoElement)
 {
-  aPseudoElement = mEvent->AsAnimationEvent()->pseudoElement;
+  aPseudoElement = mEvent->AsAnimationEvent()->mPseudoElement;
   return NS_OK;
 }
 
 } // namespace dom
 } // namespace mozilla
 
 using namespace mozilla;
 using namespace mozilla::dom;

--- a/layout/style/nsAnimationManager.h
+++ b/layout/style/nsAnimationManager.h
@@ -43,17 +43,17 @@ struct AnimationEventInfo {
     : mElement(aElement)
     , mAnimation(aAnimation)
     , mEvent(true, aMessage)
     , mTimeStamp(aTimeStamp)
   {
     // XXX Looks like nobody initialize WidgetEvent::time
     mEvent.mAnimationName = aAnimationName;
     mEvent.mElapsedTime = aElapsedTime.ToSeconds();
-    mEvent.pseudoElement =
+    mEvent.mPseudoElement =
       AnimationCollection<dom::CSSAnimation>::PseudoTypeAsString(aPseudoType);
   }
 
   // InternalAnimationEvent doesn't support copy-construction, so we need
   // to ourselves in order to work with nsTArray
   AnimationEventInfo(const AnimationEventInfo& aOther)
     : mElement(aOther.mElement)
     , mAnimation(aOther.mAnimation)

--- a/widget/ContentEvents.h
+++ b/widget/ContentEvents.h
@@ -300,26 +300,26 @@ public:
       new InternalAnimationEvent(false, mMessage);
     result->AssignAnimationEventData(*this, true);
     result->mFlags = mFlags;
     return result;
   }
 
   nsString mAnimationName;
   float mElapsedTime;
-  nsString pseudoElement;
+  nsString mPseudoElement;
 
   void AssignAnimationEventData(const InternalAnimationEvent& aEvent,
                                 bool aCopyTargets)
   {
     AssignEventData(aEvent, aCopyTargets);
 
     mAnimationName = aEvent.mAnimationName;
     mElapsedTime = aEvent.mElapsedTime;
-    pseudoElement = aEvent.pseudoElement;
+    mPseudoElement = aEvent.mPseudoElement;
   }
 };
 
 /******************************************************************************
  * mozilla::InternalSVGZoomEvent
  ******************************************************************************/
 
 class InternalSVGZoomEvent : public WidgetGUIEvent