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 simplest YouTube Video Downloader for all YouTube Flash sites, period.
Adds a download button to YouTube. By clicking on it you can download the video as a high quality mp3 file.
MORE THAN 21 MILLION DOWNLOADS
ImTranslator provides translation powered by Google Translate, Microsoft, Babylon for 70+ languages. It includes Translator, Dictionary, Text-to-Speech, Back Translation.
Video Tutorial: http://youtu.be/qyLyFkQuMGU
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.
The most lightweight and easiest translator. Translate between more than 80 languages with one click or a hot key. Translate from one word to a whole page.
LastPass, an award-winning password manager, saves your passwords and gives you secure access from every computer and mobile device.
This add-on is a downloader that lets you easily download videos from sites like Youtube, Facebook, Metacafe, Dailymotion, Break, VKontakte and music for example from SoundCloud, Grooveshark and from many other sites...
The User Agent Switcher extension adds a menu and a toolbar button to switch the user agent of a browser.
FoxyProxy is an advanced proxy management tool that completely replaces Firefox's limited proxying capabilities. For a simpler tool and less advanced configuration options, please use FoxyProxy Basic.
The Web Developer extension adds various web developer tools to the browser.
Fix the web. Gets rid of a site's cookies and LocalStorage as soon as you close its tabs. Protects against trackers and zombie-cookies. Trustworthy services can be whitelisted.