--- a/dom/events/AnimationEvent.cpp
+++ b/dom/events/AnimationEvent.cpp
@@ -43,17 +43,17 @@ AnimationEvent::Constructor(const Global
   nsCOMPtr<EventTarget> t = do_QueryInterface(aGlobal.GetAsSupports());
   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->elapsedTime = aParam.mElapsedTime;
+  internalEvent->mElapsedTime = aParam.mElapsedTime;
   internalEvent->pseudoElement = aParam.mPseudoElement;
 
   e->SetTrusted(trusted);
   return e.forget();
 }
 
 NS_IMETHODIMP
 AnimationEvent::GetAnimationName(nsAString& aAnimationName)
@@ -67,17 +67,17 @@ AnimationEvent::GetElapsedTime(float* aE
 {
   *aElapsedTime = ElapsedTime();
   return NS_OK;
 }
 
 float
 AnimationEvent::ElapsedTime()
 {
-  return mEvent->AsAnimationEvent()->elapsedTime;
+  return mEvent->AsAnimationEvent()->mElapsedTime;
 }
 
 NS_IMETHODIMP
 AnimationEvent::GetPseudoElement(nsAString& aPseudoElement)
 {
   aPseudoElement = mEvent->AsAnimationEvent()->pseudoElement;
   return NS_OK;
 }

--- a/layout/style/nsAnimationManager.h
+++ b/layout/style/nsAnimationManager.h
@@ -42,17 +42,17 @@ struct AnimationEventInfo {
                      dom::Animation* aAnimation)
     : mElement(aElement)
     , mAnimation(aAnimation)
     , mEvent(true, aMessage)
     , mTimeStamp(aTimeStamp)
   {
     // XXX Looks like nobody initialize WidgetEvent::time
     mEvent.mAnimationName = aAnimationName;
-    mEvent.elapsedTime = aElapsedTime.ToSeconds();
+    mEvent.mElapsedTime = aElapsedTime.ToSeconds();
     mEvent.pseudoElement =
       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)

--- a/widget/ContentEvents.h
+++ b/widget/ContentEvents.h
@@ -282,43 +282,43 @@ class InternalAnimationEvent : public Wi
 public:
   virtual InternalAnimationEvent* AsAnimationEvent() override
   {
     return this;
   }
 
   InternalAnimationEvent(bool aIsTrusted, EventMessage aMessage)
     : WidgetEvent(aIsTrusted, aMessage, eAnimationEventClass)
-    , elapsedTime(0.0)
+    , mElapsedTime(0.0)
   {
     mFlags.mCancelable = false;
   }
 
   virtual WidgetEvent* Duplicate() const override
   {
     MOZ_ASSERT(mClass == eAnimationEventClass,
                "Duplicate() must be overridden by sub class");
     InternalAnimationEvent* result =
       new InternalAnimationEvent(false, mMessage);
     result->AssignAnimationEventData(*this, true);
     result->mFlags = mFlags;
     return result;
   }
 
   nsString mAnimationName;
-  float elapsedTime;
+  float mElapsedTime;
   nsString pseudoElement;
 
   void AssignAnimationEventData(const InternalAnimationEvent& aEvent,
                                 bool aCopyTargets)
   {
     AssignEventData(aEvent, aCopyTargets);
 
     mAnimationName = aEvent.mAnimationName;
-    elapsedTime = aEvent.elapsedTime;
+    mElapsedTime = aEvent.mElapsedTime;
     pseudoElement = aEvent.pseudoElement;
   }
 };
 
 /******************************************************************************
  * mozilla::InternalSVGZoomEvent
  ******************************************************************************/