CSS and HTML Reference Announced by Codeburner
Users of Firefox have the choice of installing Codeburner as a Firefox add-on, or as a Firebug extension. When using the Firefox add-on, a search form is shown in the status bar that can be used to search for specific properties and elements. It displays compatibility data about the property, and users have the option to display code example in a sidebar on the same web page.
Developers will find the integration of the Firebug add-on appealing, and many developers already have Firebug installed, so adding an additional add-on won't likely be an issue.