I use Firefox as my main browser about 99% of the time, and one feature I love is the ability to extend its’ capabilities through the installation of ‘Add-ons’. One add-on that I’ve been using lately that has been a huge time saver for me is Firebug.
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.
It’s all there, all in your browser. Instant feedback on any changes you make during some CSS tweaking, etc.