My Favourite Firefox Add-Ins

AdBlock + Adblock Filterset.G
to get rid of annoying ads on web pages (yes, I know they finance themselves through ads, and I do allow those that I want to support)

del.icio.us Bookmarks
not only are my bookmarks available from everywhere - this toll also organizes them by tags and allows for searching

Firebug
essential for developers

FlashGot + Free Download Manager plugin (FDM)
a must-have for downloading stuff

FoxyProxy
allows you to use multiple proxies dependant on the URL

IE Tab
sadly, this is necessary because there are still web sites out there that render only in IE

NoScript
protection against malware

Redirect Remover
for better privacy - I hate it when search results tell the search engine, which links I followed

Session Manager
Saves your browsing sessions, in particular when FF crashes, but also whenever you wish to save so you can return later, and of course when you close FF, so you do not need to fear loosing information by closing FF any longer.

Temporary Inbox
you have to enter your email address every so often. This allows you to use a temporary email address and receive emails for verification too

Tree Style Tab
shows tabs as a tree, opens new windows from one tab as a sub-tab, and allows you to close a whole branch

Web Developer
essential for developers

YSlow
nice-to-have for developers

I also use these from time to time (nice to have): Download Statusbar, Forecastfox, Map+, Media Pirate, PDF Download, Usewr Agent Switcher