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).
With this addon you can translate any text to your own language with one click or hot-key. You can either translate the selected text, this way the translated text will overwrite the original selected text, or you can translate the full page too.
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...
A customizable mouse gestures extension which enables to execute various commands and user scripts with six types of gestures.
Advanced Eyedropper, Color Picker, Gradient Generator and other colorful goodies...
Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.
The entire page will be fading to dark, so you can watch the video as if you were in the cinema.
Block downloads, lock down bookmarks/addons/downloads with a password.
A Statusbar with speed, percentage, time and loaded size (similar to Opera's one)
Google translate gadget for firefox. This extension translates entire webpages into a language of your choice with one click. Idea comes from Google Translation Bar for Chrome.