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).
Automate Firefox. Record and replay repetitious work. If you love the Firefox web browser, but are tired of repetitive tasks like visiting the same sites every days, filling out forms, and remembering passwords, then iMacros for Firefox is the soluti...
The Web Developer extension adds various web developer tools to the browser.
Reloads web pages every so many seconds or minutes. The function is accessible via the context menu (menu you get when you right click on a web page) or via tab context menu (right click on the tab)
Use tamperdata to view and modify HTTP/HTTPS headers and post parameters...
Adds ClickOnce support and the ability to report installed .NET versions to the web server.
Advanced Eyedropper, Color Picker, Gradient Generator and other colorful goodies...
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.
This extension allows you to export your saved passwords and disabled login hosts using XML or CSV files that can be imported later.
Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.
YSlow analyzes web pages and suggests ways to improve their performance based on a set of rules for high performance web pages.
http://yslow.org is the official open source website.
LeechBlock is a simple productivity tool designed to block those time-wasting sites that can suck the life out of your working day. All you need to do is specify which sites to block and when to block them.
TinEye is a reverse image search engine. The plugin adds a context menu item that allows you to search for an image to find out where it came from, how it is being used, if modified versions of the image exist, or to find higher resolution versions.