Full Screen - Farmville

Most of the time I cannot get farmville to go into the full screen mode... Never had this problem until about 2 weeks ago. Sometimes it will go to full screen, but most of the time it will not. Farmville screen just goes Black and is frozen & I have to completely shut my browser down. With these large farms, you really need them on full screen, so this problem is driving me nuts! Any suggestions on what I can do to fix this?