Don't know why this happens, as I have not had the same problem. Why not try uninstalling your exisiting program and then do a fresh install. This quite often cures problems where programs develop glitches.
Full screen works for me but only when using Firefox. When I use IE it tells me that I need to download the flash player, which I have done on a number of occasions without success.. I also can't play any videos on YouTube when using IE, but I can when using Firefox. The common denominator therefore is FIREFOX. Good Luck.