An experimental Firefox add-on Flash Game Maximizer lets you play any online Flash Game in full screen mode even if such an option is not available in the the game.
Whenever the Flash Game Maximizer add-on detects Flash content on a web page, an icon in the status-bar glows yellow, which when clicked, toggles that Flash content to full screen view.
Note that since this is an experimental add-on, you need to login to install this. Thanks CNET.
Related: Some Wonderful Google Games