Mycroft
- Project to provide a collection of Sherlock and OpenSearch Search Engine Plugins.
- http://mycroft.mozdev.org/

Second Search
- Search by other engines directly, without switching the engine of the web-search bar.
- http://piro.sakura.ne.jp/xul/_secondsearch.html.en

The Hyperwords Project
- Allows query many web services including references, translations and conversions by selecting text.
- http://www.hyperwords.net/

TermBlaster
- Lets you do context searches on words using search engines selected by context menu.
- http://www.forizon.com/projects/termblaster/xul/

Luke's Firefox search plugins
- Search plugins for the Mozilla Firefox browser. Includes blogger user profile searches by interests, favorite music, favorite movies, and favorite books.
- http://smallcontent.n-revolt.com/firefoxplugins/

Firefox Utilities
- Includes a Site search plugin generator and many search plugins.
- http://www.7is7.com/software/firefox/

LookAhead
- Created to provide for efficient usage of time while a user performs Google searches by loading each result in its own tab.
- http://lookahead.mozdev.org/

CustomizeGoogle
- Enhance Google search results by adding links to other useful services. It can also remove ads.
- http://www.customizegoogle.com/