Once you install the plugin, you'll be able to play any of the thousands of Flash games you can find all around the Internet at fullscreen.
In order to set the game in fullscreen you'll only have to press a key and enjoy.
Not only games, but also animations and presentations if they are in Flash.
Hide status bar, adjust screen size, set diferent quality parameters,... customize the way you play Flash games.
Flash Game Maximizer is an interesting add on for Firefox, specially for games who want to enjoy Flash games like never before.