Adblock Plus – This add-on eliminate annoying content like ads from the sites that you’re visiting
Fireshot – With this add-on you can create screen-shots of web pages (entirely or just visible part)
DownThemAll! – This is a download manager/accelerator add-on for Firefox
Xmarks Bookmark and Password Sync – With this add-on you can keep your bookmarks, passwords and open tabs backed up and synchronized across computers and browsers.
Web of Trust (WOT) Safe Browsing Tool – With this add-on you can find out which websites you can trust when you search, shop and surf on the Web.