Firefox 2.x
Firefox 3.x
Windows
Mac OS X
Linux
"Firebug is a Firefox add-on that adds an impressive group of Web development tools to your browser. Displayed at the bottom of your browser or in a separate window altogether, the integrated toolbox gives you the ability to view detailed network activity, debug and execute JavaScript, edit HTML, and take full control over your CSS."
"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."


