--- a/widget/gtk/nsWindow.cpp
+++ b/widget/gtk/nsWindow.cpp
@@ -6721,16 +6721,21 @@ nsWindow::SetDrawsInTitlebar(bool aState
                                         &allocation.height);
         gtk_widget_size_allocate(GTK_WIDGET(mShell), &allocation);
 
         gtk_widget_realize(GTK_WIDGET(mShell));
         gtk_widget_reparent(GTK_WIDGET(mContainer), GTK_WIDGET(mShell));
         mNeedsShow = true;
         NativeResize();
 
+        // Label mShell toplevel window so property_notify_event_cb callback
+        // can find its way home.
+        g_object_set_data(G_OBJECT(gtk_widget_get_window(mShell)),
+                          "nsWindow", this);
+
         UpdateClientOffsetForCSDWindow();
 
         gtk_widget_destroy(tmpWindow);
     }
 
     mDrawInTitlebar = aState;
 }