diff --git a/dom/events/EventNameList.h b/dom/events/EventNameList.h
index 46ad1cae3d1..f9408ae7a0b 100644
--- a/dom/events/EventNameList.h
+++ b/dom/events/EventNameList.h
@@ -628,7 +628,7 @@ NON_IDL_EVENT(DOMFocusIn,
               EventNameType_HTMLXUL,
               eUIEventClass)
 NON_IDL_EVENT(DOMFocusOut,
-              NS_UI_FOCUSOUT,
+              eLegacyDOMFocusOut,
               EventNameType_HTMLXUL,
               eUIEventClass)
                                   
diff --git a/widget/EventMessageList.h b/widget/EventMessageList.h
index d82493d9ae2..ad94fed49a6 100644
--- a/widget/EventMessageList.h
+++ b/widget/EventMessageList.h
@@ -175,12 +175,15 @@ NS_EVENT_MESSAGE(NS_COMPOSITION_COMMIT_AS_IS, NS_COMPOSITION_EVENT_START + 4)
 // Its mRanges should be nullptr.
 NS_EVENT_MESSAGE(NS_COMPOSITION_COMMIT,       NS_COMPOSITION_EVENT_START + 5)
 
-// UI events
+// Following events are defined for deprecated DOM events which are using
+// InternalUIEvent class.
 NS_EVENT_MESSAGE(eLegacyUIEventFirst,   2500)
-// this is not to be confused with NS_ACTIVATE!
+// DOMActivate (mapped with the DOM event and used internally)
 NS_EVENT_MESSAGE(eLegacyDOMActivate,    eLegacyUIEventFirst)
+// DOMFocusIn (only mapped with the DOM event)
 NS_EVENT_MESSAGE(eLegacyDOMFocusIn,     eLegacyUIEventFirst + 1)
-NS_EVENT_MESSAGE(NS_UI_FOCUSOUT,        eLegacyUIEventFirst + 2)
+// DOMFocusOut (only mapped with the DOM event)
+NS_EVENT_MESSAGE(eLegacyDOMFocusOut,    eLegacyUIEventFirst + 2)
 
 // pagetransition events
 NS_EVENT_MESSAGE(NS_PAGETRANSITION_START, 2700)