2011 27" iMac Freezes - Fullscreen YouTube on Chrome

Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3_4 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8K2 Safari/6533.18.5)

I have a new SSD iMac. When I attempt to run YouTube movies fullscreen, it freezes. It will not allow a force quit - must hold power until it shuts down. Not totally repeatable, but happens when full screen button for movie is pressed while movie still loading.