The popular Firefox web development extension Firebug does some pretty cool stuff out of the box: debug JavaScript, tweak the CSS, and see all the network traffic.

Firebug extensions are a sort of meta-extension that lets you add on to Firebug. Developers are adding some features that we’re starting to find hard to live without.

More on:
http://www.webmonkey.com/blog/The_Five_Best_Firebug_Extensions