1. The writers for the Onion
2. The Firebug developers
3. NASA rocket scientists

Seriously though…Firebug is amazing. Quite easily the most pleasant software for development I’ve ever used. I’m sure almost everyone who ever programs in javascript/css/html out there has heard of it, but if you’ve been living under a rock and are still debugging by using alert() or something…well, you should install it. That is all.