Powermax Webdev Collection
9 Add-ons in this Collection
Firebug by Joe Hewitt, Jan Odvarko, others
The Web Developer extension adds various web developer tools to the browser.
Finds HTML elements matching chosen CSS selector(s) or XPath expression
CodeBurner is a Firefox add-on that integrates with Firebug, to extend it with reference material for HTML and CSS.
Firebug extension to view which CSS rules are actually used.
SenSEO is an extension checking the most important on-page-SEO-criteria and calculating a grade of how good your site fulfills these criteria.