Categorize: Based on the insight that bookmarks are not all equally important, provides the following features: categories, groups, menu lists, tab-sets, auto-complete and helpers to classify, organize, manage and access to bookmarks. Site contains support forum, wiki, and vast documentation about ontology problems that bookmarking presents

Firebug: Tools for web development. Allows inspect, edit and monitor CSS, HTML, JavaScript and Net requests in any web page. Includes documentation, FAQs, videos and discussion groups

Greasespot: Official Greasemonkey weblog; includes downloads, documentation, mailing list, forum and wiki

Mozilla Developer Center: Organized by topics provides documentation about extensions, themes, applications, frameworks and technologies

MozillaZine Forums : Extensions and Themes: Discussion board about releases and development of extensions and themes