Multifox is an extension that allows Firefox to connect to websites using different user names. Simultaneously! For example, if you have multiple Gmail accounts, you can open them all at the same time. Each Firefox window, managed by Multifox, accesses an account without interfering each other.
The idea behind the Application Boundaries Enforcer (ABE) module is hardening the web application oriented protections already provided by NoScript, by developing a firewall-like component running inside the browser.
Firefox Extension for interaction with Microformats
YouTube Comment Snob is a Firefox extension that filters out undesirable comments from YouTube comment threads based on criteria such as selling and cpitalization.
Fuzzbot is a native Firefox plug-in that uses librdfa for it's processing back-end. It is most useful for detecting embedded semantic information in web pages and performing actions on that semantic data.
Shows filetypes of link targets with little icons
FF extension to detect and exports microformats