dialogs with the default style mask bit set (and only that bit) should have a reasonable window class. b=222488 r=mento

widget/src/mac/nsMacWindow.cpp

@@ -355,10 +355,13 @@ nsresult nsMacWindow::StandardCreate(nsIWidget *aParent,
           switch (aInitData->mBorderStyle)
           {
             case eBorderStyle_none:
-            case eBorderStyle_default:
               windowClass = kModalWindowClass;
               break;
 
+            case eBorderStyle_default:
+              windowClass = kMovableModalWindowClass;
+              break;
+
             case eBorderStyle_all:
               windowClass = kDocumentWindowClass;
               attributes = kWindowCollapseBoxAttribute |