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 Web Developer extension adds various web developer tools to the 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.
Collector's Note Must have
Use tamperdata to view and modify HTTP/HTTPS headers and post parameters...
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.
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.
FirePHP enables you to log to your Firebug Console using a simple PHP method call.
Not using Firebug 1.9+ on Firefox 8+? See http://firephp.org/
The extension previously known as GooglePreview. Inserts preview images (thumbnails) and popularity ranks of web sites into the Google, Yahoo, Bing and DuckDuckGo search results pages.
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)
Finds HTML elements matching chosen CSS selector(s) or XPath expression
Firecookie is an extension for Firebug that makes possible to view and manage cookies in your browser
Firecookie is part of Firebug since Firebug 1.10
Note from Mozilla: This add-on has been discontinued. Try WebMail Notifier instead.
The original notifier for Gmail.
Collections are groups of related add-ons that anyone can create and share.Explore Collections