Using GTK2, latest CVS
When in full-screen mode, clicking on the full-screen button will return to the browser correctly, but it will also click on whatever was on the desktop beneath the fullscreen button.
For example, in Ubuntu, there is a panel with the trash can in the bottom right. Clicking on the full screen button opens the trash can.
Unrelated, when returning from fullscreen, an error about gtk_widget_reparent appears.
The call should be commented out in plugin.cpp:2944 (another call in the same file is already commented).