Mashable.com created a list of 30 Firefox extensions for web developers and designers. To be honest, you really only need two: Firebug and the Web Developer Toolbar. These two extensions incorporate nearly every other extension listed, and who wants to manage 28 separate extensions when they could just use two.

If you are still digging through source code by hand, then do yourself a favor and get to know Firebug. You’re job will never be the same again.