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 Javascr ipt live in any web page... Firebug 1.4 requires Firefox 3.0 or higher.
Firebug 1.5 supports Firefox 3.5 and Firefox 3.6. Please add links from these features to instructions on how to use them. See also below for More Details.