Execute windowed flash content inside Xul panel

I recently tried moving my browser from a regular window to a Xul panel, since this would give me more control over the look and feel of the application. 

Everything works quite well, except that Flash videos on Youtube won't be displayed at all (embedded Youtube videos and Flash ads work well). 

While audio can be heard, there's no video and right clicking on the Flash frame area won't lead to anything. 

I assume Youtube tries to access the windowed flash plugin, which doesn't work with panels or popups. Is there any way to get windowed plugins to work with Xul panels?