Sometimes the notification from the browser comes before the FX is completely initialized, so the "Glass Window" eventHandler is still null. In this case the position update event is ignored and the correct position is not set.
In Glass we have a same timer which calls checkScreenLocation ones in a while for child windows, but on Mac this does not work for the following reasons:
1. For "Plugin window" the eventHandler is never set, so we do not even need to check the screen location
2. For "Glass Window" the checkScreenLocation returns incorrect values, because if the correct bounds are set to the "Plugin window" by the plugin too early, they are not propagated to the "Glass Window" when it's created.

There are a number of things the correct fix should do:
1. Evaluate if the checkScreenLocation if even needed and certainly avoid creating it for the "Plugin Window".
2. Ensure that the correct location set by the plugin is propagated to the "Glass Window" and not reset back to dummy values but the window initialization code.