--- a/dom/events/Event.cpp
+++ b/dom/events/Event.cpp
@@ -172,17 +172,17 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(Ev
       }
       case eClipboardEventClass:
         tmp->mEvent->AsClipboardEvent()->clipboardData = nullptr;
         break;
       case eMutationEventClass:
         tmp->mEvent->AsMutationEvent()->mRelatedNode = nullptr;
         break;
       case eFocusEventClass:
-        tmp->mEvent->AsFocusEvent()->relatedTarget = nullptr;
+        tmp->mEvent->AsFocusEvent()->mRelatedTarget = nullptr;
         break;
       default:
         break;
     }
   }
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mPresContext);
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mExplicitOriginalTarget);
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mOwner);
@@ -215,18 +215,18 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(
         NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mEvent->clipboardData");
         cb.NoteXPCOMChild(tmp->mEvent->AsClipboardEvent()->clipboardData);
         break;
       case eMutationEventClass:
         NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mEvent->mRelatedNode");
         cb.NoteXPCOMChild(tmp->mEvent->AsMutationEvent()->mRelatedNode);
         break;
       case eFocusEventClass:
-        NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mEvent->relatedTarget");
-        cb.NoteXPCOMChild(tmp->mEvent->AsFocusEvent()->relatedTarget);
+        NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mEvent->mRelatedTarget");
+        cb.NoteXPCOMChild(tmp->mEvent->AsFocusEvent()->mRelatedTarget);
         break;
       default:
         break;
     }
   }
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mPresContext)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mExplicitOriginalTarget)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOwner)

--- a/dom/events/FocusEvent.cpp
+++ b/dom/events/FocusEvent.cpp
@@ -33,29 +33,29 @@ FocusEvent::GetRelatedTarget(nsIDOMEvent
   NS_ENSURE_ARG_POINTER(aRelatedTarget);
   NS_IF_ADDREF(*aRelatedTarget = GetRelatedTarget());
   return NS_OK;
 }
 
 EventTarget*
 FocusEvent::GetRelatedTarget()
 {
-  return mEvent->AsFocusEvent()->relatedTarget;
+  return mEvent->AsFocusEvent()->mRelatedTarget;
 }
 
 void
 FocusEvent::InitFocusEvent(const nsAString& aType,
                            bool aCanBubble,
                            bool aCancelable,
                            nsGlobalWindow* aView,
                            int32_t aDetail,
                            EventTarget* aRelatedTarget)
 {
   UIEvent::InitUIEvent(aType, aCanBubble, aCancelable, aView, aDetail);
-  mEvent->AsFocusEvent()->relatedTarget = aRelatedTarget;
+  mEvent->AsFocusEvent()->mRelatedTarget = aRelatedTarget;
 }
 
 already_AddRefed<FocusEvent>
 FocusEvent::Constructor(const GlobalObject& aGlobal,
                         const nsAString& aType,
                         const FocusEventInit& aParam,
                         ErrorResult& aRv)
 {

--- a/widget/ContentEvents.h
+++ b/widget/ContentEvents.h
@@ -208,26 +208,26 @@ public:
                "Duplicate() must be overridden by sub class");
     InternalFocusEvent* result = new InternalFocusEvent(false, mMessage);
     result->AssignFocusEventData(*this, true);
     result->mFlags = mFlags;
     return result;
   }
 
   /// The possible related target
-  nsCOMPtr<dom::EventTarget> relatedTarget;
+  nsCOMPtr<dom::EventTarget> mRelatedTarget;
 
   bool mFromRaise;
   bool mIsRefocus;
 
   void AssignFocusEventData(const InternalFocusEvent& aEvent, bool aCopyTargets)
   {
     AssignUIEventData(aEvent, aCopyTargets);
 
-    relatedTarget = aCopyTargets ? aEvent.relatedTarget : nullptr;
+    mRelatedTarget = aCopyTargets ? aEvent.mRelatedTarget : nullptr;
     mFromRaise = aEvent.mFromRaise;
     mIsRefocus = aEvent.mIsRefocus;
   }
 };
 
 /******************************************************************************
  * mozilla::InternalTransitionEvent
  ******************************************************************************/