Add-ons

QuickNote by Leszek Życzkowski, Jed Brown, others

A simple note-taking extension.

UnMHT by arai_a

UnMHT allows you to view MHT (MHTML) web archive format files, and save complete web pages, including text and graphics, into a single MHT file in Firefox/SeaMonkey.

Color Transform by Peter J. Sloetjes, MSc.

Transform the colors of entire web pages or selected elements. Combine predefined themes with basic transforms. Save transforms for specific web domains.

Torrent Tornado by Oleksandr

A Torrent Client for Firefox and SeaMonkey, runs everywhere, created in pure JavaScript without binary software!

Mozilla Archive Format, with MHT and Faithful Save by Christopher Ottley, Paolo Amadini

— Open web pages saved with Internet Explorer or other browsers (MHT)
— Save many tabs, video and audio reliably, in a single ZIP file (MAFF)
— Return to the original site you saved a page from, and more!

Notepad (QuickFox) by InBasic, J Benthum

Everyday note-taking solution.

Bluhell Firewall by Diego Casorran

Get a faster browsing experience by blocking nasty web resources using Bluhell Firewall, the lightweight Ad-Blocker and Tracking/Privacy Protector.

Linkification by y5

Converts text links into genuine, clickable links...

AutoPager by Wind Li

AutoPager automatically loads next pages when you reach the end of a page. It works on a ton of sites,Google,Yahoo..
It works well with most other add-ons adblock plus, WOT and most of the greasemonkey scripts.
You can also try AutoPagerLite.

Colorific by Peter J. Sloetjes, MSc.

Colorize entire web pages. Configure themes using sliders and drag-and-drop. Set domain preferences for automatic coloration.

Mozilla Labs Test Pilot by mart3ll