FireScope is a Firefox add-on that integrates with Firebug, to extend it with reference material for HTML and CSS. The extension's core functionality is centered around a new Reference panel, which contains a search tool for looking up HTML elements, attributes, and CSS properties.
Stuff I depend on as a webmaster and web developer (all on one page) Go home. A text only version is also available. Number of resources currently on this page: 326 in 45 sections. Thanks to all who have suggested