404: File Not Found
Basically works like the Internet Wayback Machine
Adblock Plus
Hurr
ChatZilla
IRC!
Download Statusbar
Downloads appear at the bottom of your window in a little customizable bar, instead of that big window.
PDF Download
Gives you options about PDFs you get linekd to from websites before they open/download/etc.
Popup Alt Attrib
I... don't actually remember.
;
Snaplinks
Allows you to rightclick and hold, and drag-draw a box around webpages. Any links in the box open as tabs.
StumbleUpon
Semi-random website service; You input categories you're interested in and it grabs random user provided sites that match that tag. Custom tags avaliable!
Tab Mix Plus
Gives you more options with your Firefox Tabs
Uppity
Click a button, move up a level in the HTML address of a website you're viewing (
http://www.blah.com/whatever ->
http://www.blah.com)
Also, I have some themes! But whatever.