--- a/content/events/src/nsDOMEvent.cpp
+++ b/content/events/src/nsDOMEvent.cpp
@@ -664,17 +664,17 @@ nsDOMEvent::DuplicatePrivateData()
         new WidgetCommandEvent(false, mEvent->userType,
                                oldCommandEvent->command, nullptr);
       commandEvent->AssignCommandEventData(*oldCommandEvent, true);
       newEvent = commandEvent;
       break;
     }
     case NS_UI_EVENT:
     {
-      InternalUIEvent* oldUIEvent = static_cast<InternalUIEvent*>(mEvent);
+      InternalUIEvent* oldUIEvent = mEvent->AsUIEvent();
       InternalUIEvent* uiEvent =
         new InternalUIEvent(false, msg, oldUIEvent->detail);
       uiEvent->AssignUIEventData(*oldUIEvent, true);
       newEvent = uiEvent;
       break;
     }
     case NS_SVGZOOM_EVENT:
     {
@@ -682,17 +682,17 @@ nsDOMEvent::DuplicatePrivateData()
       WidgetGUIEvent* guiEvent = new WidgetGUIEvent(false, msg, nullptr);
       guiEvent->eventStructType = NS_SVGZOOM_EVENT;
       guiEvent->AssignGUIEventData(*oldGUIEvent, true);
       newEvent = guiEvent;
       break;
     }
     case NS_SMIL_TIME_EVENT:
     {
-      InternalUIEvent* oldUIEvent = static_cast<InternalUIEvent*>(mEvent);
+      InternalUIEvent* oldUIEvent = mEvent->AsUIEvent();
       InternalUIEvent* uiEvent = new InternalUIEvent(false, msg, 0);
       uiEvent->eventStructType = NS_SMIL_TIME_EVENT;
       uiEvent->AssignUIEventData(*oldUIEvent, true);
       newEvent = uiEvent;
       break;
     }
     case NS_SIMPLE_GESTURE_EVENT:
     {

--- a/content/events/src/nsDOMUIEvent.cpp
+++ b/content/events/src/nsDOMUIEvent.cpp
@@ -39,18 +39,17 @@ nsDOMUIEvent::nsDOMUIEvent(mozilla::dom:
   }
   
   // Fill mDetail and mView according to the mEvent (widget-generated
   // event) we've got
   switch(mEvent->eventStructType)
   {
     case NS_UI_EVENT:
     {
-      InternalUIEvent *event = static_cast<InternalUIEvent*>(mEvent);
-      mDetail = event->detail;
+      mDetail = mEvent->AsUIEvent()->detail;
       break;
     }
 
     case NS_SCROLLPORT_EVENT:
     {
       InternalScrollPortEvent* scrollEvent = mEvent->AsScrollPortEvent();
       mDetail = (int32_t)scrollEvent->orient;
       break;

--- a/content/smil/nsDOMTimeEvent.cpp
+++ b/content/smil/nsDOMTimeEvent.cpp
@@ -21,18 +21,17 @@ nsDOMTimeEvent::nsDOMTimeEvent(mozilla::
   if (aEvent) {
     mEventIsInternal = false;
   } else {
     mEventIsInternal = true;
     mEvent->eventStructType = NS_SMIL_TIME_EVENT;
   }
 
   if (mEvent->eventStructType == NS_SMIL_TIME_EVENT) {
-    InternalUIEvent* event = static_cast<InternalUIEvent*>(mEvent);
-    mDetail = event->detail;
+    mDetail = mEvent->AsUIEvent()->detail;
   }
 
   mEvent->mFlags.mBubbles = false;
   mEvent->mFlags.mCancelable = false;
 
   if (mPresContext) {
     nsCOMPtr<nsISupports> container = mPresContext->GetContainer();
     if (container) {