2 866 444 users
281 767 users
LastPass, an award-winning password manager, saves your passwords and gives you secure access from every computer and mobile device.
749 244 users
The Web Developer extension adds various web developer tools to the browser.
311 573 users
Advanced Eyedropper, Color Picker, Gradient Generator and other colorful goodies...
205 777 users
View HTTP headers of a page and while browsing.
147 743 users
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.
86 327 users
HTML Validator is a Mozilla extension that adds HTML validation inside Firefox and Mozilla. The number of errors of a HTML page is seen on the form of an icon
For Firefox 23+, you need 0.958 (under review)
Collections are groups of related add-ons that anyone can create and share.Explore Collections