I haven’t posted here in a while, but I just came off this great screencast of the super-duper Firefox extension that is Firebug. If you haven’t seen Firebug before, and you do any HTML/Javascript/CSS work, you should check it out. From the getfirebug.com website:
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.
Nifty! (found via Veerle)