SiteLauncher is a Firefox add-on that gives you a super-quick way to to open your favorite websites using only your keyboard. One special hotkey brings up the Launcher, followed by a unique key to launch a site. It's highly customizable - colors, font sizes, and transparency can all be changed. If you'd prefer a wide display, you can use up to eight columns. Don't like rounded corners? Square them off.
More info: SiteLauncher