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!
LastPass, an award-winning password manager, saves your passwords and gives you secure access from every computer and mobile device.
Displays a country flag depicting the location of the current website's server and provides a multitude of tools such as site safety checks, whois, translation, similar sites, validation, URL shortening, and more...
Xmarks is the #1 bookmarking and open tab add-on. Keep your bookmarks, and open tabs backed up and synchronized across computers and browsers. Mobile phones with Premium access. Utilize LastPass to sync passwords!
When you find something on the web that you want to view later, put it in Pocket. It automatically syncs to your phone, tablet or computer so you can view it at any time, even without an internet connection.
Use PDF Download to do whatever you like with PDF files on the Web. Regain control and eliminate browser problems, view PDFs directly in Firefox as HTML, and use the all-new Web-to-PDF toolbar to save and share Web pages as high-quality PDF files.
Visual bookmarks for Firefox. (Works with all latest versions of Firefox)
Allows editing of web page content while in Print Preview mode, prior to printing or saving as HTML or PDF. Compacts the layout and removes unwanted content such as adverts, sidebars and blank pages. Any element can be formatted, hidden or deleted.
A Statusbar with speed, percentage, time and loaded size (similar to Opera's one)
Automatically find user scripts on Userscripts.org (requires Greasemonkey or Scriptish)
Add useful extra features to Gmail, like hierarchical labels, an unread message icon on your browser tab, file attachment icons, and more.