History Tree

Find any page you have visited quickly and easily. Shows your browsing history as a tree of tabs, with thumbnail screenshots of the web-pages in every tab you have opened.

Tab Scope

Preview and navigate tab contents through popup.

Tab Control

Take control of your tabs! Purposely lightweight extension with the following features...

ShareThis

ShareThis makes sharing any online content quick and easy. The ShareThis plugin allows you to share to any contact via email, text message, Facebook, Twitter and more. You can also store your shares for later to reshare with the ShareThis ShareBox.

FirePalette

Adds a color picker to Firebug's CSS panel.

Tab History Menu

When click on the selected tab, a history menu corresponding to it will display.

SyncPlaces

Synchronizes your bookmarks, passwords and password exceptions between browsers. Uses your own (or third party) web or ftp server so you have complete control and privacy.

CSS Usage

Firebug extension to view which CSS rules are actually used.

Inline Code Finder for Firebug

Inline Code Finder is an add-on to Firebug, to be able to find HTML elements

Provides some additional capabilities to firebug to find inline code as opposed to external files.

Save Complete

Saves a webpage completely, providing a better alternative to the flawed built-in save functionality of Firefox.

Another of my personal favorites, modifies the "Save complete page" option of firefox to truly be more complete, I don't understand why firefox doesn't already do this.

FireDownload

The FireDownload extension for Firefox and Wyzo lets you manage and accelerate your web downloads up to 10x faster! With FireDownload, download acceleration is seamlessly displayed within the downloads window. Try the ultimate download accelerator!

Pretty nice and unobtrusive download enhancer.

Xmarks BYOS Edition

Bookmark Sync "Bring Your Own Server" Edition (BYOS). For expert users who wish to sync their bookmarks and passwords using their own FTP or WebDAV server.

FormBug

An extension to Firebug to make dealing with forms easier

Widerbug

Firebug Evolved.

SyntaxHighlighter

a syntax highlighter, based on SyntaxHighlighter(http://code.google.com/p/syntaxhighlighter/), support lots of program languages.

Adds syntax highlighting, somewhat intensive.

Total Validator

Perform multiple validations and take screen shots in one go. This 5-in-1 validator works with external, internal, or local web pages using the Total Validator service or local copy of the desktop tool...

ReloadEvery

Reloads web pages every so many seconds or minutes. The function is accessible via the context menu (menu you get when you right click on a web page) or via a drop down menu on the reload button ...

Love this plugin, replaces the reload button with a look-alike button with a drop-down menu that lets you enable automatic reloading of a tab (or all tabs) and set the number of seconds between reloads. I've found it very useful for checking cookie behaviour and cache setups, its also nice if you want to keep checking a page for updates.

Window Resizer

Resize your browser to various standard resolution sizes...

Quickly resize your window to the common sizes to see what a site looks like for users with that resolution.

Font Finder

Get all CSS styles of selected text in Firefox / Thunderbird...

Locate the fonts that are in use on a webpage. Small and unobtrusive.

FireQuery

Firebug enhancements for jQuery (requires Firebug 1.3+)

Adds jquery support, I usually keep disabled even though I personally use jquery for web development.

Alexa Sparky

Alexa Internet's official add-on for Firefox! Get Alexa data in your status bar.

Shows the alexa rank of a site, I like it but it does make new HTTP requests for each page, so I disable it alot for privacy or speed.

Dust-Me Selectors

Finds unused CSS selectors.

One of the newer add-ons I've been using. Lets you find which CSS rules are actually in use on a page, thus helping you to minimize and streamline CSS. Very cool but it is a little resource intensive so by default I keep it disabled.

ToggleUseDocColors

Toggles Tools->Options->Content->Colors:Allow pages to choose their own colors... option with a single keystroke (Ctrl+M)

Use the documents colors or other.

FoxTor

FoxTor: Anonymous Web Browsing using the encrypted TOR network...

Bing

This is the only officially supported Bing add-on, provided by the Bing team in Microsoft. Bing is a search engine that finds and organizes the answers you need so you can make faster, more informed decisions.

Inline Code Finder

Inline Code Finder is a tool to traverse through all elements in a web page, and when it finds a HTML element with any of these, it will highlight them: * Inline JavaScript events * Inline style * javascript: links

MM3-ProxySwitch

In the Firefox Browser (and other Mozilla programs) you can per default configure only the setting for one internet connection. With the MM3-ProxySwitch you can manage different configurations and simply switch over between these.

If like me you often connect to websites by proxying firefox through SSH Tunnels, then you can use this MM3-ProxySwitch add-on to run 3 different instances of firefox (by using multiple firefox profiles) that EACH use a different Proxy. This is useful if you want to MAX out your download speed by downloading using multiple tunnels to do the work.

Also useful for just plain multiple proxy configurations, very easy, and super extremely unobtrusive and low-resource intensive.

Firecookie

Firecookie is an extension for Firebug that makes possible to view and manage cookies in your browser

One of my personal favorites, adds a tab to firebug that lets you view live cookies being set, deleted, and updated, and lets you edit, and delete cookies of a page LIVE.

RESTClient

RESTClient is a firefox extension use to visit and test RESTful/WebDav services.

Java Console 6.0.02

Java Console Extension for Java SE 1.6.0_02 (version 6 update 2).

RSS Ticker

RSS Ticker loads your Live Bookmarks and scrolls their entries across your screen while you surf.

Amazingly awesome add-on that scrolls rss feeds across a small area, helpful to keep track of various feeds and your own sites feeds.

Tab Sidebar

Displays previews of your tabs in your sidebar.

I like this one more than the tab preview add-ons, lets me find a tab quickly but only when I want by opening the sidebar.

CryptoFox

CryptoFox is an encryption/decryption tool for Mozilla Firefox, with dictionary attack support for cracking MD5 passwords.

Bookmark Current Tab Set

Adds options to quickly bookmark all tabs in a window and store them in a bookmark folder that is given the date (and optionally the time) as its name.

Update Scanner

Monitors web pages for updates. Useful for websites that don't provide Atom or RSS feeds.

Image Zoom

Adds zoom functionality for images...

Simple image zooming functionality. Small and useful add-on.

FaviconizeTab

This extension adds a new "FaviconizeTab" option to the context menu of the tab...

Nice to Faviconize your most-often-used sites

CacheViewer

This extenion is GUI Front-end of "about:cache"...

Just a shortcut to the about:cache area.

FireGestures

A customizable mouse gestures extension which enables you to execute various commands and user scripts with five types of gestures.

Firebug Net History Panel Overlay

Adds history functionality to firebug net panel. Requires Firebug 1.2.0b4 or 1.2.0b6 For Firebug versions 1.1.* please use Net Panel Add-on Version 0.2.1

Add Bookmark Here ²

Add a menuitem "Add Bookmark Here..." to Bookmarks...

DNS Cache

Allows you to disable and enable the DNS Cache of Firefox

The final caching add-on that I absolutely LOVE. Lets you add anywhere on your toolbar to clear the DNS cache of firefox. I have this, clear cache, and clear cookies next to each other on the far left of my bookmarks toolbar, I use them ALOT.

Manage Folders

Places a "Manage Folder" item on the context menu of bookmark folders, which opens the "Places Organizer" expanded to that folder.

View Dependencies

View Dependencies adds a tab to the Page Info window, in which it lists all the files which were loaded to show the current page.

Torbutton

Torbutton provides a button to securely and easily enable or disable the browser's use of Tor. It is currently the only addon that will safely manage your Tor browsing to prevent IP address leakage, cookie leakage, and general privacy attacks.

Quick way to switch firefox to use the TOR network (I recommend the free vidalia suite) which is useful for web developers that rely on an IP address in certain programming and setups.

Tab Kit

Tab grouping, vertical tab tree, multi-rows, and various tweaks for power users.

QuickRestart

Ever needed to restart Firefox after enabling or disabling an extension, switching to a new theme, or modifying configuration files (such as userChrome.css or user.js)? This simple extension adds a "Restart Firefox" item to the "File" menu. You can also use the Ctrl+Alt+R keyboard shortcut, or the included toolbar button.

A button you can place anywhere that restarts the browser just like you do after updating add-ons.

Organize Status Bar

This extension will enable you to organize your status bar icons. You can now rearrange or remove any item (icon or text) in the Firefox status bar. If your status bar is full and cluttered like mine was, give this a try.

Lets you rearrange the items on the status bar.

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.

FEBE

FEBE (Firefox Environment Backup Extension) allows you to quickly and easily backup your Firefox extensions. In fact, it goes beyond just backing up -- It will actually rebuild your extensions individually into installable .xpi files. Now you can easily synchronize your office and home browsers.

Very helpful and well-designed add-on that lets you backup your entire firefox, or individual add-ons, or both!

Check Places

Checks your bookmarks are valid and the pages still exist. Also checks for duplicates and for empty folders and can restore missing favicons.

All-in-One Sidebar

All-in-One Sidebar (AiOS) is an award-winning sidebar control, inspired by Opera's. It lets you quickly switch between sidebar panels, view dialog windows such as downloads, extensions, and more in the sidebar, or view source or websites in the sidebar.

GMarks

GMarks helps you sync & manage your bookmarks with Google Bookmarks...

Add-on Collector

There's a new way to manage and find favorite add-ons. Comment, share, and sync collections, all from your browser.

Lets you get updates and makes it very easy to browse a collection such as this one.

Advanced Dork:

Advanced Dork: gives quick access to Google's Advanced Operators directly from the context menu...

Very unobtrusively makes the advanced google search operators available.

Yahoo! Toolbar

Use Yahoo! and the web faster, safer, and easier with new mail notification, search suggestions, online bookmarks, free spyware scanning, and more... Save time with the new Yahoo! Toolbar 2.0, now in beta at toolbar.yahoo.com/beta.

Email This!

Email This! will send your recipient the link, title, & highlighted text of the page you are viewing using GMail, Google Apps GMail, Yahoo, and Stand-Alone Mail Clients like Outlook Express, Thunderbird, & More! If you hate toolbar buttons don’t fret because I've included a right-click pop-up menu and access keys!

Tab To Window

Open a tab in a new window...

I have wanted this type of functionality for soo long.

Cache View

Cache View is a Firefox extension that displays Google's Cache, Coral's Cache, and Wayback Machine's Cache cache of an open tab or selected link via a right-click or the Tools menu.

Useful to notice how often a page on your site is crawled and cached by these engines.

Lazarus: Form Recovery

Never lose anything you type into a web form again! Lazarus securely auto-saves all forms as you type, so after a crash, server timeout, or whatever, you can go back to the form, right click, "recover form", and breathe a sigh of relief.

Saves your form data securely as you enter it, and provides a way to recover that form data if your firefox crashes (more likely windows crashes) and that way you won't lose anything you already entered. This will slow down firefox alot though.

Tab Preview

Preview tab contents on mouseover

Multirow Bookmarks Toolbar

Multi Row Bookmarks Toolbar.

Googlepedia

Shows you a relevant Wikipedia article along with your search results. Clicking links in the article will trigger new Google searches, making it a very useful research tool...

Adds wikipedia results right next to google results, very helpful to keep an eye on what is authoritative, and often get the best information fast.

QuickJava

Allows quick enable and disable of Java and Javascript from...

Undo Closed Tabs Button

Tired of going to History -> Recently Closed Tabs just to undo a closed tab? Then this extension is for you! This extension allows you to undo closed tabs via a toolbar and/or tab bar button or the right-click context menu.

One of my personal favorites, adds back the most recently closed tab, very helpful.

Faviconiac Search Engines

Adds PNG favicons to some search engines and web directories, such as Google, Yahoo, Bing, Ask, Altavista, Wikipedia, AOL, Dmoz, Alexa, del.icio.us and others.

This is helpful to get a better feel for search engine results by adding their sites favicon to the search results page, is somewhat HTTP Request intensive however.

Bookmark This Page Plus

Adds a menu item in each sub folder of the bookmarks menu to bookmark the current page. Just as seen in the Opera browser.

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 toolbar button to perform this operation. It displays the status of operation in the status bar.

This is invaluable, it removes all the cookies from whichever domain you are currently viewing.

Modify Headers

Add, modify and filter http request headers. You can modify the user agent string, add headers to spoof a mobile request (e.g. x-up-calling-line-id) and much more. Take a look at the help tab of the Modify Headers window...

Pretty awesome, lets you modify the HTTP Headers your browser is sending, useful to check accessibility, server settings, language settings, etc.

OPML Support

OPML Support adds OPML import/export functionality to the Firefox Bookmarks manager.

HttpFox

An HTTP analyzer addon for Firefox

FoxTab

3D in your browser! FoxTab brings innovative 3D functionality to your Firefox.

Super awesome cool. If your machine is fast this is a really helpful add-on.

View Source Chart

View Source In Color-Coded Chart Get V2.8 w/ a brand new feature from jennifermadden.com

One of my long-time, all-time favorites that lets you view the source code of a website, but in a color-coded and formatted view. Very nice and helpful for (X)HTML developers.

Smart Bookmarks Bar

Not enough place on your bookmarks bar ?... Smart Bookmarks Bar extension comes right here by hiding bookmarks names and only showing icons. Bookmark names will be displayed on mouse over.

For those who frequently use the bookmarks in the firefox bookmarks toolbar, this is a great way to show more in a cleaner way.

Extended Statusbar

A Statusbar with speed, percentage, time and loaded size (similar to Opera's one)

Provides much more information unobtrusively on your statusbar, very cool!

Email Yourself!

Email Yourself! allows you to email yourself the link, title, and a selected summary of the webpage you are viewing using GMail.

SwitchProxy Tool

SwitchProxy lets you manage and switch between multiple proxy configurations...

LiveClick

Adds feed reading, notifications, favicons, and other enhancements to Live Bookmarks.

Places' Tooltips

This addon enhances all the tooltips in Firefox.

Multi Smart Search

"Multi smart search" displays a new context menu including all the installed search engine.

SortPlaces

Sorts your bookmarks in a variety of ways.

Flashblock

Never be annoyed by a Flash animation again! Blocks Flash so it won't get in your way, but if you want to see it, just click on...

Lets you block flash for all/specific websites/domains, which is pretty nice capability to test both your sites for non-flash viewers, and speeds up firefox.

Google Toolbar

Take the power of Google with you anywhere on the Web

A great add-on that lets you use hundreds of google tricks and tools. Very helpful but also makes a lot of background HTTP requests so privacy-conscious or speed-freaks will want it disabled.

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 hierarchy can be navigated using a two-paned window that allows for a variety of different views on the document and all nodes within. Note: This add-on depends on binary changes to Firefox, and will not work with Firefox 2.

Way to inspect the DOM of a page, useful for web developers.

Stay-Open Menu

Enables multiple selections from Bookmarks Menu, History Menu, or Smart Location Bar (awesomebar) dropdown list, without reopening menu or using sidebar.

Menu Editor

Customize application menus: Rearrange or remove menuitems from the main context menu (right-click menu) and main menubar (File Edit View etc.)

Multiple Tab Handler

Provides feature to close multiple tabs.

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.

An advanced java script console.

Bookmark Previews

Bookmark Previews adds an album view and thumbnail view to the bookmarks manager.

Now this one is what I call genius. Lets you view previews of your bookmarks! Great if like me you have over a thousand bookmarks.

LastPass Password Manager

LastPass is a free online password manager and Form Filler that makes your web browsing easier and more secure. LastPass supports IE and Firefox as Plugins (Opera, Safari, Chrome, iPhone, Opera Mini via Bookmarklets), allows you to import from every major password storage vendor and export too, captures passwords that other managers won't including many AJAX forms, and allows you to make strong passwords easily. Your sensitive data is encrypted _locally_ before upload so even LastPass cannot get access to it. One Time Passwords & Screen Keyboard help protect your master password.

What can I say, this add-on is in my top 10 for sure, and I recommend it to all my friends and even my family. Lets me create very secure passwords for sites that I don't have to remember because lastpass remembers them for me, and stores them encrypted on both a usb medium I keep, and on their servers. So when I use someone elses computer or reinstall firefox, I have all my usernames and passwords, and its just sooooooooooooooooo useful. Get this add-on, it truly is a secure way to only have to remember 1 password from now on, thus LastPass. The last password you need.

Tabs Open Relative

Tabs Open Relative makes all new tabs open to the right of the current tab, rather than at the far right of the tab bar (optionally this only applies to links).

This stops that annoying default of opening tabs wayy on the right.

Coral IE Tab

An enhanced version of IE Tab which enables you to use the embedded IE engine within tabs of Mozilla Firefox. It supports Adblock Plus in IE, and can sync cookies between IE and Firefox.

Tamper Data

Use tamperdata to view and modify HTTP/HTTPS headers and post parameters...

Useful for checking form validation and security, lets you tamper data! lol

YSlow

YSlow analyzes web pages and why they're slow based on Yahoo!'s rules for high performance web sites. YSlow uses Yahoo!'s Smush.it service, which is subject to Smush.it Terms of Use: http://info.yahoo.com/legal/us/yahoo/smush_it/smush_it-4378.html

One of the top 3 most important and helpful add-ons for firefox. Web Developers who don't use this one are simply irresponsible.

MeasureIt

Draw out a ruler to get the pixel width and height of any elements on a...

ColorZilla

Advanced Eyedropper, ColorPicker, Page Zoomer and other colorful goodies...

A must-have add-on for anyone using CSS or developing websites, very amazing, highly capable add-on. The one issue is that is is somewhat of a resource-hog.

Greasemonkey

Allows you to customize the way a webpage displays using small bits of JavaScript. ...

Lets you use user-contributed javascripts (or your own of course) that modifies the behavior and/or appearance of many different websites.

FireFTP

FireFTP is a free, secure, cross-platform FTP client for Mozilla Firefox which provides easy and intuitive access to FTP servers.

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. * Requires Firebug

Web Developer

The Web Developer extension adds a menu and a toolbar with various web developer tools.

This add-on is 1 of the top 2 most important add-ons for web developers. The other is firebug.

Firebug

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... Firebug 1.4 requires Firefox 3.0 or higher.

By far, without a doubt, the single most important and valuable add on for ANY web developer. This is the one that is definitely required. The features are too numerous to name here.

Live HTTP Headers

View HTTP headers of a page and while...

Very helpful for those that don't have and use wireshark.

FoxyProxy

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.

The most complete proxifying tool for firefox, multiple configurations possible.

SearchStatus

Display the Google PageRank, Alexa rank, Compete ranking and SEOmoz Linkscape mozRank anywhere in your browser, along with fast keyword density analyser, keyword/nofollow highlighting, backward/related links, Alexa info and more.

Adds a very unobtrusive way to check the pagerank, and several other SEO statistics but only when you click a button (if configured that way) very helpful occasionally.

DownThemAll!

The first and only download manager/accelerator built inside Firefox!

Very nice, easy, fast, and unobtrusive add-on that lets you download all files of a certain type to a certain save location, lets you use builtin filters or configure your own using basic REGEX. Very helpful.

Clear Cache Button

Adds a clear cache toolbar button. After installing the extension, find the clear cache button in the toolbar customization...

A button you can add to your toolbar that clears your firefox cache (not cookies or history) which is invaluable for web developers.

Wolfram Alpha Google

Display Wolfram Alpha results in Google searches. No need to switch search engines when you can use both at once!

The new search is a glimpse at the future of computing.

Personal Menu

"Menus Toolbar" item is now available in Toolbar Context Menu and you may hide it forever!

Lets you go beyond firefox builtin menu editing and create a custom toolbar.

Jiffy

Adds a new panel to Firebug for displaying timing measurements for JavaScript applications.

Adds the ability to time or profile your javascript, I usually leave disabled.

FireRainbow

Javascript syntax highlighting for Firebug 1.3+

Fire.fm

Fire.fm gives you access to the extensive music library on Last.fm. Last.fm gives free radio to the US, UK, and Germany, plus subscriber-based service to the rest of the world. Listen to your favorite music and discover new artists in the process.

What would work be without free streaming music that is customizable and recommends music based on your history. Conveniently can be added to your status bar, or your toolbar.

StumbleUpon

StumbleUpon discovers web sites based on your interests, learns what you like and brings you more.

StumbleUpon is great. Very cool way to see relevant and interesting web development articles and sites.