Add-ons

Session Manager by Michael Kraft

Session Manager saves and restores the state of all or some windows - either when you want it or automatically at startup and after crashes. It can also automatically save the state of open windows individually.

ReminderFox by Tom Mutdosch, Daniel Lee, others

ReminderFox displays and manages lists of reminders and tasks. ReminderFox uses easy-to-use lists with warnings/alarms to remind you of all your important appointments.
Synchronize ReminderFox with other calendars as well.

Thumbnail Zoom Plus by David Adler

Shows full image when you hover over a thumbnail. Works with Amazon, Baidu Images, Bing Images, Facebook, Flickr, Google+, Google Images, IMDb, LinkedIn, Netflix, Pinterest, Reddit, Twitter, Yandex, YouTube, Wikipedia, Yahoo Images, & many more.

UnPlug by h2g2bob

UnPlug is an extension which lets you save video and audio which is embedded on a webpage - it's a video download tool.

CuteButtons by ChoGGi

Adds icons to buttons and/or menus.

Google Privacy by Herrminator

Make some popular websites respect your privacy settings.
Please see the known issues below!

Urban Dictionary by kefka781

Search using Urban Dictionary

SweetSearch by Mark Moran

SweetSearch is A Search Engine for Students. It searches only trustworthy, credible Web sites, and avoids the clutter you find in other search engines. It is particularly useful for biographies, history, and other research assignments.

Medical Spell Checker with OpenMedSpel by e-MedTools

OpenMedSpel for Mozilla Firefox, Thunderbird, and SeaMonkey is free and open source medical spell checking dictionary that includes nearly 50,000 medical terms ranging from abdominis to zygomatic.

HashColouredTabs+ by John P Baker

Improves tab identification by providing a small colored icon for any site which doesn't have its own 'site icon'.
★ 'favicon' now also shown in history and bookmarks ★

Futuristic City - -Star Wars Like by manishp100

Russian blue Green Eyes watching you by tekarts

Leopard at the moon by Chibusia