Lifehack has a list of the Top 10 Firefox extensions to improve your productivity.

Out of these 10 I just use 3 (FlashGot, FlashBlock and Tab Mix Plus) but I think I’ll give some of the others a try as well.

Download Statusbar Firefox extension

Download Statusbar looks useful to me

I would add the Web Developer and NoScript (doesn’t improve your productivity much but gives you some protection against junk scripts running on certain sites).