Web Developer
lots of great tools for web developers
FireBug
more granular debugging, better console, and more tools for JS coders
User Agent Switcher
lets you send a different useragent string
Tab Mix Plus
adds a bunch of great functionality to firefox tabs (making them almost as good as opera tabs)
Live Http Headers
report of http requests generated for a given page
IE Tab
embeds the IE control in a firefox tab. good for pixel comparisons
ScrapBook
grabs pages and all their assets, rewriting links to work from a local file
Dated: 01/09/2007