Only a few - Maybe
Flashgot -
http://www.flashgot.net
Extremely useful download manager integration program. Easily download specific, all, or selected files and have your favorite download manager download them
BugMeNot -
http://www.bugmenot.com
Excellent tool for getting past those "Must sign up, BUT ITS FREEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEeeeeeeeeeeeeeeeeeeeeeeee" sites
Nuke Anything Enhanced -
https://addons.mozilla.org/firefox/951/
Good for nuking anything... Right click on something and tell it to go away. Very cool tool for temporarily or permanently removing objects on a page. Is completely manual though, so it won't seek out things to remove. Thats not a huge problem though, as it works hand in hand with any other ad/flash blockers that have already been listed. If it gets through the blocker, just tell Nuke to get rid of it. Superb for removing crap before printing so you just have a small clean page to print
PDF Download -
http://www.pdfdownload.org/
Nice extension to tell firefox what to do with that PDF file you just downloaded. It's hard to explain, but it just makes dealing with downloading PDF files easier. Try it, delete it if you don't like it.
Tab Mix Plus -
https://addons.mozilla.org/firefox/1122/
The sexiest advanced tab extension for me. Includes all the usual tab functions, but includes a browser crash restore feature and more.
Adblock Plus -
http://adblockplus.org
Blocks ads. and stuff! Be sure to get a good filter list to import, otherwise you will not be blocking much right after the install
McAfee SiteAdvisor -
http://www.siteadvisor.com/
Nice search engine and site helper. It won't make your searches any better, and it definitely won't improve any sites you visit. What it does is if the site is clean without problems (FOR YOU), might be dangerous to visit, or better off leaving alone. Integrates with Google and other major search engines to tell you if a search result is more or less safe, and will tell you if the current page you are on is safe.
- Will tell you WHY it failed the safety test as well if you click on the status bar link, or the siteadvisor lights next to each search result
- tfproject.org is a safe site
Chatzilla -
http://www.hacksrus.com/~ginda/chatzilla/index.html
Because sometimes you just don't want to use mIRC (or whatever you are currently using that isn't already Chatzilla)