Firebug
If you are a Firefox user and a web developer you will get a lot of use out of Firebug. With this addon “You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.”
From the site:
Inspect and edit HTML
Firebug makes it simple to find HTML elements buried deep in the page. Once you’ve found what you’re looking for, Firebug gives you a wealth of information, and lets you edit the HTML live.
