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).
Restyle the web with Stylish, a user styles manager. Stylish lets you easily install themes and skins for Google, Facebook, YouTube, Orkut, and many, many other sites. You can even customize Firefox and other programs themselves.
A customizable mouse gestures extension which enables to execute various commands and user scripts with six types of gestures.
Adds the ability to create and edit entries in the password manager.
Make any pages' search functionality available in the Search Bar (or "search box")...
Customize your bookmarks bar with Roomy Bookmarks Toolbar
Make sure your tabs stay visible all the time.
Extends smooth scroll more tweakable. By keyboard scroll also supported.
Customizes the new tab page. Add more tiles. Add the launcher from Firefox start. Have a background image. Set new tile images and titles. See recently closed tabs. And more...
Personalize Firefox Button in Firefox 4 and change it to your personal and powerful one!
Create your personalized menu to replace Menu Bar in Firefox 3.
Save links, images and web pages to user-defined folders and their sub-folders straight from context menu.