Basic Extensions, includes Firebug
Designer Extensions
Developer Extensions
Network Performance Extensions
Firebug Labs Extensions

Firebug The Firebug Working Group

The Firebug Web Page Debugger, Firefox version more info

Eventbug Jan 'Honza' Odvarko and John J. Barton

This extension brings a new Events panel that lists all of the event handlers on the page grouped by event type. The panel also nicely integrates with other Firebug panels and allows to quickly find out, which HTML element is associated with specific event listener or see the Javascript source code. more info

Firediff Kevin Decker

Firediff is a Firebug extension that tracks changes to a pages DOM and CSS. more info

SelectBug

List elements for each CSS selector, trial CSS selectors by typing them in.

NetExport Jan 'Honza' Odvarko

Allows exporting data from the Net panel. more info

FireCookie Jan 'Honza' Odvarko

View and manage cookies in your browser more info

Illuminations for Developers Steven Roussey

Enhances Firebug to understand JavaScript libraries and frameworks (like ExtJS, Dojo Toolkit, SproutCore, Closure Library, qooxdoo, YUI3, and jQuery/jQueryUI), making things more obvious and helpful when debugging. Trial version. more info

FirePHP

Log to your Firebug Console from PHP (FirePHP< 1.0) more info

FireStarter

extends Firebug's activation model with advanced features.

FBTest

Test Driver for Firebug Itself, useful for extension authors

Tested with Firebug