http://www.getfirefox.com is a nice download site now for Firefox.
Once in a while, I get asked what extensions I use and whenever I do a system buildup that I'm going to be using personally, I always grab these and they work with 1.5 already.
AdBlock Plus -
http://p2.forumforfree.com/releases-vf3-adblockplus.html - This blocks most annoying web "features" of some websites.
Filterset.G Updater -
http://www.pierceive.com/ - Autoupdating ad filter list for AdBlock Plus
FasterFox -
http://fasterfox.mozdev.org/ - Tweaks a few common settings inside FF that I normally tweak anyway - Yes I know it breaks RFC specs if you fully enable it, but setting any of the HTTP max requests over 8 is pointless because FireFox is hardcoded to not go over 8 even if you specify a number above that.
Nightly tester tools -
http://users.blueprintit.co.uk/~dave/web/firefox/buildid/nightly.html - Extension fixer-upper - Most people won't need this one but I typically run either the Branch trunks of the FireFox builds when a new release is coming out or sometimes I have other profiles that I use to run the Trunk builds when I feel like living dangerous. This forces potentially non-working extensions to run under new builds even if they might break your build. I used to manually edit the extensions, but not anymore!
