Cooliris, this is really cool for browsing images on Google
https://addons.mozilla.org/en-US/firefox/addon/5579
One of my friends is a developer of that add-on.
security & privacy
-NoScript - the best for controlling active content, hence security, most adds
-RequestPolicy - like NoScript but controls communication between Firefox and websites
-CS Lite - per site cookie management
-Adblock - block adds
-FlashBlock - replace flash content with a placeholder clickable to play
browser enhancements
-DownThemAll-download manager
-Download Helper - save Flash movies to your computer
-Tabs Open Relative - opening a link in a new tap opens next to the current tab
-Session Manager - save and restore browser windows and sessions
-FEBE - backup your extensions
-CLEO - turn all of you backuped extensions into a single installable
General
-Forcastbar Enhanced - a weather forecast bar w/animated doppler radar
-Scrapbook - save exact copies of wep pages
-PrintPDF - print web page as PDF
-CoolIris - very slick picture viewer
-Sage - RSS feed reader
-Webmail Notifier - check various webmail accounts
-MyCroft - for adding hundreds of other possible search engines to the search bar (Amazon, Craigslist, Pricegrabber, YouTube, etc.)