Blocks annoying video ads on YouTube, Facebook ads, banners and much more.
Adblock Plus blocks all annoying ads, and supports websites by not blocking unobtrusive ads by default (configurable).
The first and only download manager/accelerator built inside Firefox!
The best security you can get in a web browser!
Allow active content to run only from sites you trust, and protect yourself against XSS and Clickjacking attacks.
Download all the links, movies and audio clips of a page at the maximum speed with a single click, using the most popular, lightweight and reliable external download managers.
Organize your schedule and life's important events in a calendar that's fully integrated with your Thunderbird email. Manage multiple calendars, create your daily to do list, invite friends to events, and subscribe to public calendars.
OpenPGP message encryption and authentication for Thunderbird and SeaMonkey.
ReminderFox displays and manages lists of reminders and ToDo's. ReminderFox makes sure you remember all of your important dates via easy-to-use lists, alerts, and alarms, right in your browser without the need for a separate calendar program.
StumbleUpon is the easiest way to discover new and interesting photos, videos, web pages and more, recommended by a community of experts. Tell us what you are interested in and we recommend page after page of amazing stuff you’d never expect to see.
Add useful extra features to Gmail, like hierarchical labels, an unread message icon on your browser tab, file attachment icons, and more.
NewsFox is an efficient 3-pane(email) style Atom/RSS feed reader.
ScribeFire Classic is a blog editor that integrates with Firefox and lets you easily post to your blog.
ScribeFire Classic is no longer supported; you should install ScribeFire Next: https://addons.mozilla.org/en-US/firefox/addon/scribefire-next