CodeBurner for Firebug Requires Restart
CodeBurner is a Firefox add-on that integrates with Firebug, to extend it with reference material for HTML and CSS.
MeasureIt Requires Restart
Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.
This extension provides a list to almost all the settings that you may need to alter in order to enhance Firefox's speed.
HackBar Requires Restart
Simple security audit / Penetration test tool.
Easily override the browser's User-Agent string
React Developer Tools is a tool that allows you to inspect a React tree, including the component hierarchy, props, state, and more. To get started, just open the Firefox devtools and switch to the React tab.
Discover what runs a website - This Firefox extension helps you identify technologies used on any website at the click of a button.
ColorfulTabs Requires Restart
The first addon you should be installing on a fresh Firefox install. A must have. The most beautiful yet the simplest add-on that makes a strong colorful appeal. Colors every tab in a different color.
Firefinder for Firebug Requires Restart
Finds HTML elements matching chosen CSS selector(s) or XPath expression
Accelerate your SEO efforts on the fly. SEOquake is a free plugin for browsers that provides you with key SEO metrics for a specific page, along with other useful tools such as SEO Audit and many others.
The easiest way ever to change IP and browse anonymously! Just activate it with one click and it's done, you're browsing the web with a random HTTP or Socks proxy list from several countries in the world. No ads. 100% free to prevent web censorship.
Gives you a place to put all your add-on buttons without over-crowding the navigation bar.
Open current page or link in tor browser for better privacy
Quickly and easily switch between popular user-agent strings.
View JSON documents in the browser.
a customizable extension to save the images from the current tab page
View HTTP headers of a page and while browsing.
This is an unofficial "Live HTTP headers" clone, mainly to fix the Replay feature!
Advanced Cookie Manager Requires Restart
A must have tool for Web Developers and Testers to Manage and monitor web cookies.
Export / Backup
Import / Restore
Available in English, French, Spanish, German and Italian languages.