If you are a Mac user, and you are anything like me, you go back and forth between Firefox and Safari as your primary browser. Firefox for its Add Ons, such as Firebug. And, Safari for its Mac-esque-nes.
One "must have" Safari feature for me, was the ability to bind a keyboard shortcut to a bookmark that is in your Bookmarks Bar. It is possible that you did not even know of this feature. If you put a bookmark into your Bookmarks Bar, Safari will give it a Comand+<number> keyboard short cut.
Well, now, Firefox has something just as awesome! SiteLauncher: https://addons.mozilla.org/en-US/firefox/addon/10127
On a Mac, you hit control+alt. A sweet looking HUD appears. Hit a key. Opens a site.