firefox add-ons

My favourites:

Adblock Plus
Add to Search Bar
AlertBox
DownloadHelper
DownThemAll
FEBE
Gmail Checker
LastPass
Long URL Please Mod
NoScript
Xmarks

DownThemAll and Chatzilla very nice

just adblock

The bookmark add on is great incase you need to reinstall Firefox

Tab Mix Plus
Text Link
Xmarks
Firegesturers
Downthemall
Chatzilla
Auto Copy
Bookmark duplicate detector
Download status bar
FEBE
PDF Download
Nightly tester tools
Flashblock

I think they are enough :P

Very important add-ons are ADBlock Plus,Noscript,Betterprivacy and Flagfox.The rest are only useful if you need it!

for me
adblock
chatzilla
firebug
noscript
i've tested more in the past but these are the most needed for me

Search for AddonFox. It has the most used addons in it. It's a great to be honest.

Down Them all is a nice add-on for Firefox

I think NoScript is the best and most needed add-on.

I used to use various add-on's for things like additional tab options/customization, tab session saving, hyperlinking plain text, and extra downloading options, but after multiple times of reinstalling firefox, I find that I don't always go back to them or bother looking for them. Plus everytime a new Firefox comes out, it seems like multiple add-on's are then no longer supported and you have to find a replacement or an equivalent. At one point I had a ton of tab sessions saved with an add-on and I think I lost them all due to that. I also remember one of the original tab option customization add-on's being discontinued when Firefox v2 first came out.