20 Firefox Extensions for Web Developers

Firefox is a widely-used browser – not just by users but web developers. Simply put, Firefox and its addons can make developing for the web easier and simpler. And with the release of Firefox 4, it got even easier. This article features 20 essential Firefox addons for web developers.

Before diving into the Firefox addons, though, here’s a quick glimpse into some of the noteworthy new Firefox features that benefit web developers:

  • Improved HTML5: Gecko now uses the HTML5 parser, which fixes bugs, improves interoperability, and improves performance.
  • Better CSS support: Firefox 4 features support for new CSS transitions, computed values, selector grouping, background image subrectangle, and touch properties.
  • New CSS stuff: Firefox 4 adds new CSS properties, pseudo-classes, pseudo-selectors, and functions.
  • More graphics and video support: for WebGL, WebM video, SMIL animation for SVG, and more.
  • Better DOM support: for JavaScript typed arrays, touch and multi-touch events, and more.
  • Improved security: new security features added like Content Security Policy (CSP), HTTP Strict Transport Security, and more.
  • Built-in developer tool: Firefox 4 features the Web Console tool which is a debugging aid for web and extension developers.

However, what makes Firefox great is the development community around it, and appropriately there are tons of addons that make your web development simpler and easier.
Please note that four of the extensions below are still marked as ‘experimental’, but have been tested and do work perfectly well with Firefox 4, they are: HTML5toggle, HTML5 Validator, Mobile Toolkit and Mobilify.


FireFTP is a free, secure, cross-platform FTP/SFTP client for Mozilla Firefox which provides easy and intuitive access to FTP/SFTP servers. Along with transferring your files quickly and efficiently, FireFTP also includes more advanced features such as: directory comparison, syncing directories while navigating, SFTP, SSL encryption, search/filtering, integrity checks, remote editing, drag & drop, file hashing, and more.
Download FireFTP

HTML5toggle (Experimental)

HTML5toggle provides a button which makes it easy to turn on or off the HTML5 support in Firefox 4. Given that HTML5 support is still evolving, some websites do not work as expected when HTML5 support in Firefox 4 is enabled.
Download HTML5toggle

HTML5 Validator (Experimental)

HTML5 Validator adds a ‘HTML 5 Validator’ context menu item to a page’s context menu.
Download HTML5 Validator

IE Tab 2

IE Tab 2 lets you use IE to display web pages in a tab within FireFox. Adopted from the original IE Tab, this version has new features including IE 7, 8 or 9 compatibility modes. You can also import settings from your old IE Tab.
Download IE Tab 2

Total Validator

Total Validator lets you perform multiple validations and take screen shots in one go.
Download Total Validator

Web Developer

Web Developer adds various web developer tools to Firefox.
Download Web Developer


EditCSS is a stylesheet modifier in the Sidebar.
Download EditCSS


Console² replaces the JavaScript Console with what could be the next generation Error Console. Console² let’s you display errors filtered by type (Errors, Warnings, Messages), language (JavaScript, CSS, XML) and context (Chrome, Content).
Download Console²

CSS Reloader

CSS Reloader allows you to reload all the CSS of any site without you have to reload the page itself.
Download CSS Reloader

View Source Chart

View Source Chart lets you inspect the DOM—and learn HTML—at lightning speed.
Download View Source Chart

Screenshot Pimp

Screenshot Pimp has a silly name but a useful function: it lets you capture, grab, save, download, or copy anything you see in your web browser—and beyond—with only one click.
Download Screenshot Pimp

Mobile Toolkit (Experimental)

MobileToolkit helps you to validate the code of any page, check it on several mobile emulators and find documentation to improve your mobile compatibility. It offers not only one click code validation but also mobile render emulation for various mobile devices and browsers.
Download Mobile Toolkit


Firebug integrates with Firefox to put a wealth of development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.
Download Firebug

CodeBurner for Firebug

CodeBurner integrates with Firebug to extend it with reference material for HTML and CSS.
Download CodeBurner for Firebug

Adobe BrowserLab for Firebug

Adobe BrowserLab integrates with Firebug and generates screenshots of your pages (public or behind a firewall) in multiple browsers. Launch Adobe BrowserLab directly from Firebug and preview temporary changes you’ve made using Firebug.
Download Adobe BrowserLab for Firebug

FirePath for Firebug

FirePath integrates with Firebug and adds a development tool to edit, inspect and generate XPath 1.0 expressions, CSS 3 selectors and JQuery selectors (Sizzle selector engine).
Download FirePath for Firebug

Firepicker for Firebug

Firepicker integrates with Firebug and adds a small color picker dialog when editing a CSS rule in Firebug. Firepicker scans for values that can be parsed as CSS colors (#abc, rgb(1,2,3), blue, red etc.) and displays them in a drop-down list right below the firebug’s CSS editor box. Clicking on the color value in the drop-down brings up a color picker dialog.
Download Firepicker for Firebug


iMacros lets you automate Firefox. Whatever you do with Firefox, iMacros can record and replay that repetitious work so you don’t have to manually do it each time.
Download iMacros


FoxyProxy is an advanced proxy management tool that completely replaces Firefox’s limited proxying capabilities. It automatically switches an internet connection across one or more proxy servers based on URL patterns.
Download FoxyProxy

What Are Your Essential Web Developers Firefox 4 Addons?

Over to you: what are your favorite Firefox 4 addons for web developers? Feel free to share your useful additions in the comments section below.