Speed up the development process by using add-ons to troubleshoot, edit, and debug web projects without ever clicking away from Firefox.
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.
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.
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.
FireFTP is a free, secure, cross-platform FTP/SFTP client for Mozilla Firefox which provides easy and intuitive access to FTP/SFTP servers.
Check out my new project, FireSSH!
Advanced Eyedropper, Color Picker, Gradient Generator and other colorful goodies...
Firefox OS Simulator is a test environment for Firefox OS. Use it to test your apps in a Firefox OS-like environment that looks and feels like a mobile phone. After installing it, go to Web Developer > Firefox OS Simulator to access its features.
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.
Color tools for web development.
Color picker and eyedropper + saving colors and trying out colors with drag and drop.
Show the IP address(es) of the current page in the status bar. It also allows querying custom information services by IP (right click) and hostname (left click), like whois, netcraft, etc. Additionally you can copy the IP address to the clipboard.