Firebug integrates with Firefox to put a wealth of web development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.

Features:
· Just the way you like it Firebug is always just a keystroke away, but it never gets in your way. You can open Firebug in a separate window, or as a bar at the bottom of your browser. Firebug also gives you fine-grained control over which websites you want to enable it for.
· Inspect and edit HTML
· Tweak CSS to perfection
· Visualize CSS metrics
· Explore the DOM
· Execute JavaScript on the fly
· Monitor network activity
· Debug and profile JavaScript
· Quickly find errors
· Logging for JavaScript

· Back/Forward buttons keyed to Control-Shift Left,Right arrows
· Breakpoints saved across Firefox sessions
· Font changes in the command line

Download: FireBug 1.6.10 Alpha (1.1 MB) | FireBug 1.5.4 (1.1 MB) | Screenshot | Homepage