GEO Source Code

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

Visit the Firebug website for documentation, screen shots, and discussion forums: http://www.getfirebug.com

or

https://addons.mozilla.org/en-US/firefox/addon/1843