Sometimes it won't work, especially after you go in and come out of it. When this happens, go to the tab in the toolbar, right-click on it and click restore. Then hit F11 to get back.
On a side note broy-I would suggest trying the Chrome browser. It's free, installs easily and the game really plays well on it. I went there to verify what I told you above and forgot how slow it is sometimes. It's my default browser but I play golf in Chrome. JMO