Firebug for Firefox 3

[#1]

This is an addon that  you may find very useful if you are creating webpages it Firbug for Firefox FREE from
https://addons.mozilla.org/en-US/firefox/addon/1843
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...
Its a great tool and may help debug pages you have a problem with

[#2]

Another Firefox extension I found useful is Web Developer: https://addons.mozilla.org/en-US/firefox/addon/60