Bug 297080. Mouse exit events from top-level windows should always be treated as exit events even if the cursor is still within window bounds (it must have moved into an on-top window). r+sr=bzbarsky,a=bsmedberg

content/events/src/nsEventStateManager.cpp

@@ -451,19 +451,29 @@ nsEventStateManager::PreHandleEvent(nsPresContext* aPresContext,
     break;
   case NS_MOUSE_EXIT:
     // If the event coordinate is within the bounds of the view,
-    // then it's not really an exit --- we may have traversed
-    // widget boundaries but we're still in our toplevel window.
-    if ((aView->GetBounds() - aView->GetPosition()).Contains(aEvent->point)) {
-      // treat it as a move so we don't generate spurious "exit"
-      // events Any necessary exit events will be generated by
-      // GenerateMouseEnterExit
-      aEvent->message = NS_MOUSE_MOVE;
-      // then fall through...
-    } else {
-      GenerateMouseEnterExit((nsGUIEvent*)aEvent);
-      //This is a window level mouse exit event and should stop here
-      aEvent->message = 0;
-      break;
+    // and this is not the top-level window, then it's not really
+    // an exit --- we may have traversed widget boundaries but
+    // we're still in our toplevel window.
+    // On the other hand, if we exit a toplevel window, then
+    // it's really an exit even if the mouse is still in the
+    // window bounds --- the mouse probably moved into some
+    // "on top" window.
+    {
+      nsMouseEvent* mouseEvent = NS_STATIC_CAST(nsMouseEvent*, aEvent);
+      nsCOMPtr<nsIWidget> parentWidget = getter_AddRefs(mouseEvent->widget->GetParent());
+      if (parentWidget &&
+        (aView->GetBounds() - aView->GetPosition()).Contains(aEvent->point)) {
+        // treat it as a move so we don't generate spurious "exit"
+        // events Any necessary exit events will be generated by
+        // GenerateMouseEnterExit
+        aEvent->message = NS_MOUSE_MOVE;
+        // then fall through...
+      } else {
+        GenerateMouseEnterExit((nsGUIEvent*)aEvent);
+        //This is a window level mouse exit event and should stop here
+        aEvent->message = 0;
+        break;
+      }
     }
   case NS_MOUSE_MOVE:
     // on the Mac, GenerateDragGesture() may not return until the drag