NPNVxDisplay for windowless plugins should not return the Display* of an XtBin. b=444252 r+sr=jst

modules/plugin/base/src/ns4xPlugin.cpp

@@ -2188,9 +2188,13 @@ _getvalue(NPP npp, NPNVariable variable, void *result)
 #ifdef MOZ_WIDGET_GTK2
     if (npp) {
       ns4xPluginInstance *inst = (ns4xPluginInstance *) npp->ndata;
-      NPBool rtv = PR_FALSE;
-      inst->GetValue((nsPluginInstanceVariable)NPPVpluginNeedsXEmbed, &rtv);
-      if (rtv) {
+      PRBool windowless = PR_FALSE;
+      inst->GetValue(nsPluginInstanceVariable_WindowlessBool, &windowless);
+      NPBool needXEmbed = PR_FALSE;
+      if (!windowless) {
+        inst->GetValue((nsPluginInstanceVariable)NPPVpluginNeedsXEmbed, &needXEmbed);
+      }
+      if (windowless || needXEmbed) {
         (*(Display **)result) = GDK_DISPLAY();
         return NPERR_NO_ERROR;
       }