Super Mario Bros 3: Crazy Firefox theme of the day
Normally I don't really like tinkering with my theme, because the colors are such a stark contrast to the web page you are viewing and the buttons are usually some crazy weird new symbol that will take you some getting use to. But this theme has a light color to it, so navigating around the web is easier on the eyes.
This theme has all of the pull-down menus and pop-up menus changed to match the idea behind the Super Mario Brother games. My favorite part about this theme is that all of the slide bars are warp pipes. And then, once you get your theme installed and set, you gotta play the flash Super Mario Brothers game!