One of the goals of Firefox have always been to make the lives of web developers as easy and productive as possible, by providing tools and a very extensible web browser to enable people to create amazing things. The idea here is to list a lot of the tools and options available to you as web developers using Firefox.
Native developer tools in Firefox
We are working on building a great set of developer tools for you included in Firefox. They are described much more in detail in Developer Tools in Firefox Aurora 10 and there are some very interesting implications for what we can accomplish with them!
We are evaluating and experimenting with a number of user interfaces and code approaches to try and find the most optimal ways to work with code in a page. If you install Firefox Aurora you can try them out right now! Let us know what you think.

Also stay tuned to this blog, since we will post updates on progress and features for the native Developer Tools.
Firebug
By far, the most well-known web developer tool in a web browser is the Firebug extension, and without a doubt, for a long time it set the bar for how web developing and debugging should be. Firebug is still a very important tool with lots of powerful features, including a vast number of extensions (see below).
Just something you need to be aware of, though, is with everything that Firebug offers it can be quite heavy when it comes to consuming memory, so use it accordingly.
Firefox extensions for web developers
Over the years, a lot of extensions have been developed to help web developers utilize Firefox to the maximum. Some of the most used and well-known are these ones, but please let us know if we have missed any that helps you!
        Accessibility Evaluation Toolbar
    
     Support web developers in testing web resources for accessibility features.
Support web developers in testing web resources for accessibility features.
        All in One Sidebar
    
     AiOS lets you open various windows as sidebar panels, and quickly switch between them. So it put an end to the window chaos! In addition to bookmarks and history it opens dialogues such as downloads, add-ons and more in the sidebar.
AiOS lets you open various windows as sidebar panels, and quickly switch between them. So it put an end to the window chaos! In addition to bookmarks and history it opens dialogues such as downloads, add-ons and more in the sidebar.
        Cache Status
    
     Easy cache status & management from status.
Easy cache status & management from status.
        CacheToggle
    
     Disable (and optionally clear) the browser cache with the flick of a switch.
Disable (and optionally clear) the browser cache with the flick of a switch.
        Colorzilla
    
     Advanced Eyedropper, ColorPicker, Gradient Generator and other colorful goodies.
Advanced Eyedropper, ColorPicker, Gradient Generator and other colorful goodies.
        Console²
    
     Console² (pronounced Console Squared or Console Two) replaces the JavaScript Console with what could be the next generation Error Console. From v0.5 includes the Console Filter extension previously available separately from the Console² website.
Console² (pronounced Console Squared or Console Two) replaces the JavaScript Console with what could be the next generation Error Console. From v0.5 includes the Console Filter extension previously available separately from the Console² website.
        CSS Reloader
    
     CSS Reloader is an extension that allows you to reload all the CSS of any site without you have to reload the page itself.
CSS Reloader is an extension that allows you to reload all the CSS of any site without you have to reload the page itself.
        DOM Inspector
    
     DOM Inspector is a tool that can be used to inspect and edit the live DOM of any web document or XUL application. The DOM can be navigated using a two-paned window displaying a variety of different views on the document and all nodes within.
DOM Inspector is a tool that can be used to inspect and edit the live DOM of any web document or XUL application. The DOM can be navigated using a two-paned window displaying a variety of different views on the document and all nodes within.
        Firefogg
    
     Video and audio encoding for Firefox. With Firefogg you can encode most media files to Ogg and WebM. Firefogg also provides an API to integrate encoding into the upload process.
Video and audio encoding for Firefox. With Firefogg you can encode most media files to Ogg and WebM. Firefogg also provides an API to integrate encoding into the upload process.
        FireFTP
    
     FireFTP is a free, secure, cross-platform FTP/SFTP client for Mozilla Firefox which provides easy and intuitive access to FTP/SFTP servers.
FireFTP is a free, secure, cross-platform FTP/SFTP client for Mozilla Firefox which provides easy and intuitive access to FTP/SFTP servers.
        FireUnit
    
     JavaScript Unit Testing Extension
JavaScript Unit Testing Extension
        FoxGuide
    
     Display horizontal and vertical floating guides, exactly the way you use it in photoshop. Helps improving layout, placing elements in proper grids, laying out elements symmetrically and structure a design.
Display horizontal and vertical floating guides, exactly the way you use it in photoshop. Helps improving layout, placing elements in proper grids, laying out elements symmetrically and structure a design.
        FoxyProxy Standard
    
     FoxyProxy is an advanced proxy management tool that completely replaces Firefox’s limited proxying capabilities. It offers more features than SwitchProxy, ProxyButton, QuickProxy, xyzproxy, ProxyTex, TorButton, etc.
FoxyProxy is an advanced proxy management tool that completely replaces Firefox’s limited proxying capabilities. It offers more features than SwitchProxy, ProxyButton, QuickProxy, xyzproxy, ProxyTex, TorButton, etc.
        Geolocater
    
     Geolocate you where you want.
Geolocate you where you want.
        GreaseMonkey
    
     Customize the way a web page displays or behaves, by using small bits of JavaScript.
Customize the way a web page displays or behaves, by using small bits of JavaScript.
        HTML Validator
    
     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.
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.
        HttpFox
    
     An HTTP analyzer addon for Firefox.
An HTTP analyzer addon for Firefox.
        iMacros for Firefox
    
     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 solution you’ve been dreaming of!
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 solution you’ve been dreaming of!
        Jenkins Build Monitor
    
     Monitor Jenkins (http://jenkins-ci.org) builds and display the status on Firefox status bar.
Monitor Jenkins (http://jenkins-ci.org) builds and display the status on Firefox status bar.
        jQuery extension
    
     jQuery and jQuery UI embedded in browser.
jQuery and jQuery UI embedded in browser.
        JSONovich
    
     Pretty-prints JSON content in the browser for easy, unobtrusive viewing.
Pretty-prints JSON content in the browser for easy, unobtrusive viewing.
        JSONView
    
     View JSON documents in the browser.
View JSON documents in the browser.
        JSView
    
     If the website you are viewing contains any external js/css files, an icon will appear that says “SS”, “JS”, or both. Each individual file can then be viewed by clicking on the filename. The file will be opened in a new window.
If the website you are viewing contains any external js/css files, an icon will appear that says “SS”, “JS”, or both. Each individual file can then be viewed by clicking on the filename. The file will be opened in a new window.
        Link Widgets
    
     Eases navigation within sequences of pages (e.g. Web comics, forums, or technical specifications such as the HTML 4 Recommendation) by providing toolbar buttons for the first, previous, next, and last page.
Eases navigation within sequences of pages (e.g. Web comics, forums, or technical specifications such as the HTML 4 Recommendation) by providing toolbar buttons for the first, previous, next, and last page.
        Live HTTP Headers
    
     View HTTP headers of a page and while browsing.
View HTTP headers of a page and while browsing.
        LiveReload
    
     LiveReload refreshes a web page when files change.
LiveReload refreshes a web page when files change.
        MeasureIt
    
     Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.
Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.
        Modify Headers
    
     Add, modify and filter the HTTP request headers sent to web servers. This addon is particularly useful for Mobile web development, HTTP testing and privacy.
Add, modify and filter the HTTP request headers sent to web servers. This addon is particularly useful for Mobile web development, HTTP testing and privacy.
        NoScript
    
     The best security you can get in a web browser! Allow active content to run only from sites you trust, and protect yourself against XSS and Clickjacking attacks.
The best security you can get in a web browser! Allow active content to run only from sites you trust, and protect yourself against XSS and Clickjacking attacks.
        PageSpeed
    
   Page Speed is an open-source project started at Google to help developers optimize their web pages by applying web performance best practices.
Page Speed is an open-source project started at Google to help developers optimize their web pages by applying web performance best practices.
        Phoenix
    
   An editor with real time syntax highlighting which allows edit, run and test CSS, HTML and JavaScript code. Phoenix will tell you how many CSS and JS files are loaded into a page, how big these are, it will let you edit, pack and de-obfuscate them.
 An editor with real time syntax highlighting which allows edit, run and test CSS, HTML and JavaScript code. Phoenix will tell you how many CSS and JS files are loaded into a page, how big these are, it will let you edit, pack and de-obfuscate them.
        PixelZoomer
    
     PixelZoomer takes a screenshot of the current website and provides various tools for pixel analysis. You can zoom into websites (up to 3200%), measure distances and pick colors with an eye dropper.
PixelZoomer takes a screenshot of the current website and provides various tools for pixel analysis. You can zoom into websites (up to 3200%), measure distances and pick colors with an eye dropper.
        Pixlr Grabber
    
     Grabbing screens and pulling images from the web just got a bit easier. With the Pixlr Grabber add-on, you can copy, save, share or even edit your final grabs – including any image or background – with just a right-click.
Grabbing screens and pulling images from the web just got a bit easier. With the Pixlr Grabber add-on, you can copy, save, share or even edit your final grabs – including any image or background – with just a right-click.
        Poster
    
     A developer tool for interacting with web services and other web resources that lets you make HTTP requests, set the entity body, and content type. This allows you to interact with web services and inspect the results.
A developer tool for interacting with web services and other web resources that lets you make HTTP requests, set the entity body, and content type. This allows you to interact with web services and inspect the results.
        QuickJava
    
     Allows quick enable and disable of Java, Javascript, Flash, Silverlight, Images, Stylesheets and Proxy from the Statusbar and/or Toolbar without having to open any dialogs!
Allows quick enable and disable of Java, Javascript, Flash, Silverlight, Images, Stylesheets and Proxy from the Statusbar and/or Toolbar without having to open any dialogs!
        Rainbow Color Tools
    
     Color tools for web development. Color picker and eyedropper + saving colors and trying out colors with drag and drop.
Color tools for web development. Color picker and eyedropper + saving colors and trying out colors with drag and drop.
        Regular Expressions Tester
    
     Testing tool for regular expressions with color highlighting (including submatches) and helpers for creating expressions.
Testing tool for regular expressions with color highlighting (including submatches) and helpers for creating expressions.
        Remove Cookie(s) for Site
    
     A very simple extension to remove all the cookies of currently opened site. It adds an option to the Right Click menu of the page, and a Clear Cookies Button to perform this operation. It displays the status of operation in the status bar.
A very simple extension to remove all the cookies of currently opened site. It adds an option to the Right Click menu of the page, and a Clear Cookies Button to perform this operation. It displays the status of operation in the status bar.
        Screenshot Pimp
    
     Capture, grab, save, download, or copy anything you see in your web browser with only one click! Screenshot pimp is by far the most customizable, and user friendly screenshot toolbar available for both Windows and Mac!
Capture, grab, save, download, or copy anything you see in your web browser with only one click! Screenshot pimp is by far the most customizable, and user friendly screenshot toolbar available for both Windows and Mac!
        SQLite Manager
    
     Manage any SQLite database on your computer.
Manage any SQLite database on your computer.
        Selenium IDE Button
    
     Just one simple toolbar button to open Selenium IDE. You need to have installed Selenium IDE: http://seleniumhq.org/projects/ide/
Just one simple toolbar button to open Selenium IDE. You need to have installed Selenium IDE: http://seleniumhq.org/projects/ide/
        SeoQuake SEO extension
    
     Seoquake is a Firefox SEO extension aimed primarily at helping web masters who deal with search engine optimization (SEO), social media optimization (SMO) and internet promotion. Seoquake allows to investigate many important SEO parameters.
Seoquake is a Firefox SEO extension aimed primarily at helping web masters who deal with search engine optimization (SEO), social media optimization (SMO) and internet promotion. Seoquake allows to investigate many important SEO parameters.
        ShowIP
    
     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.
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.
        Stylish
    
     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.
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.
        Tamper Data
    
     Use tamperdata to view and modify HTTP/HTTPS headers and post parameters.
Use tamperdata to view and modify HTTP/HTTPS headers and post parameters.
        TAW3
    
     You can have an idea, with a single click, of how accesible web sites are.
You can have an idea, with a single click, of how accesible web sites are.
        Tilt 3D
    
     A WebGL-based 3D visualization of a webpage.
A WebGL-based 3D visualization of a webpage.
        Total Validator
    
     Perform many different validations in one go. This multiple validator works with external, internal, or local web pages using a local copy of the desktop tool obtained from http://www.totalvalidator.com/downloads/extensiontool.html.
Perform many different validations in one go. This multiple validator works with external, internal, or local web pages using a local copy of the desktop tool obtained from http://www.totalvalidator.com/downloads/extensiontool.html.
        TryAgain
    
     TryAgain keeps trying to load a webpage when the server cannot be reached.
TryAgain keeps trying to load a webpage when the server cannot be reached.
        User Agent Switcher
    
     The User Agent Switcher extension adds a menu and a toolbar button to switch the user agent of a browser.
The User Agent Switcher extension adds a menu and a toolbar button to switch the user agent of a browser.
        Wappalyzer
    
     Wappalyzer is a browser add-on that uncovers the technologies used on websites.
Wappalyzer is a browser add-on that uncovers the technologies used on websites.
        Web Developer
    
     The Web Developer extension adds various web developer tools to a browser.
The Web Developer extension adds various web developer tools to a browser.
Firebug extensions
There exists a lot of extensions for Firebug for a number of different use cases, and a number of them are listed here:
        Acebug
    
     Syntax highlighting for the Firebug command line using Ace. Fuzzy auto completion.
Syntax highlighting for the Firebug command line using Ace. Fuzzy auto completion.
        Code Coverage v2 for Firebug 0.1
    
     This Firebug extension is used to report the Javascript code coverage.
This Firebug extension is used to report the Javascript code coverage.
        CSS Usage
    
     Firebug extension to view which CSS rules are actually used.
Firebug extension to view which CSS rules are actually used.
        Firecookie
    
     Firecookie is an extension for Firebug that makes possible to view and manage cookies in your browser.
Firecookie is an extension for Firebug that makes possible to view and manage cookies in your browser.
        Firefinder
    
     Finds HTML elements matching chosen CSS selector(s) or XPath expression.
Finds HTML elements matching chosen CSS selector(s) or XPath expression.
        FirePHP
    
     FirePHP enables you to log to your Firebug Console using a simple PHP method call.
FirePHP enables you to log to your Firebug Console using a simple PHP method call.
        FireQuery
    
     Firebug plugin for jQuery development.
Firebug plugin for jQuery development.
        friendly bug
    
     Makes firebug friendlier and easier to use
Makes firebug friendlier and easier to use
        Inline Code Finder for Firebug
    
     Inline Code Finder is an add-on to Firebug, to be able to find HTML elements with any of these issues: Inline JavaScript events, Inline style, javascript: links.
Inline Code Finder is an add-on to Firebug, to be able to find HTML elements with any of these issues: Inline JavaScript events, Inline style, javascript: links.
        FireRainbow
    
     Javascript syntax highlighting for Firebug.
Javascript syntax highlighting for Firebug.
        NetExport
    
     NetExport is a Firebug extension that allows exporting all collected and computed data from the Net panel. The structure of the created file uses HTTP Archive (HAR) format (based on JSON).
NetExport is a Firebug extension that allows exporting all collected and computed data from the Net panel. The structure of the created file uses HTTP Archive (HAR) format (based on JSON).
        Pixel Perfect
    
     Pixel Perfect is a Firefox/Firebug extension that allows web developers and designers to easily overlay a web composition over top of the developed HTML.
Pixel Perfect is a Firefox/Firebug extension that allows web developers and designers to easily overlay a web composition over top of the developed HTML.
        YSlow
    
     YSlow analyzes web pages and why they’re slow based on Yahoo!’s rules for high performance web sites.
YSlow analyzes web pages and why they’re slow based on Yahoo!’s rules for high performance web sites.
There are even more extensions available for Firebug, available in the Firebug Extensions wiki.
About Robert Nyman [Editor emeritus]
Technical Evangelist & Editor of Mozilla Hacks. Gives talks & blogs about HTML5, JavaScript & the Open Web. Robert is a strong believer in HTML5 and the Open Web and has been working since 1999 with Front End development for the web - in Sweden and in New York City. He regularly also blogs at http://robertnyman.com and loves to travel and meet people.
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