Firefox plugin to ease openid authentication
track changes made in Firebug
Mozilla setting to have dns resolve by socks proxy host
Firebug add-on for cookie information
Lookup words in dictionary.app from firefox.
Firefox 3 PDF Viewer Plugin
Easy UI mockups in Firefox
Add S/MIME support to Gmail
Automating security when away from home
(body)
Syncs OS X system proxy settings to Firefox automatically
Adds HTML validation to View Source
Take full page, and other, shots of your websites
Adds a cookie tab to your Page Info window
watch your http headers in real time, save them, reinject
firefox content to your mobile