The add on's block advertising and you get faster loads because of that alone.  Mouse gestures allow you to browse forward and back by right clicking your mouse and moving it left or right. The dictionary tells you the meaning of unknown words. The site adviser tells you if a site is safe.  Image zoom lets you see those tiny pictures a lot bigger.  Paste and go lets you copy something and paste it into the google search and look without any extra clicks.  Reload every lets you update a page of weather info, ebay or markets without you having to click all the time. FireFTP lets you access an FTP sever to download files without an extra program. 

There are many others.  I also use Foxit reader because it's faster than Adobe and doesn't have the same security issues.  These are some of my add on's.  There are more and some you might like that I don't have.  Internet Explorer can't remotely compete with Firefox if you do more than go to a couple of sites.