This is probably where to begin.

Rather useful insights into browser usage.

"A prototype that encrypts and securely synchronizes the Firefox experience across multiple browsers, so that your desktop, laptop, and mobile phone can all work together. It currently supports continuous synchronization of your bookmarks, browsing history, saved passwords and tabs."

"An experimental add-on to explore geolocation in Firefox 3 ahead of the implementation of geolocation in a future product release. Geode provides an early implementation of the W3C Geolocation specification so that developers can begin experimenting with enabling location-aware experiences using Firefox 3 today, and users can tell us what they think of the experience it provides."

"A Firefox extension that works with FEBE* to package any number of extensions/themes into a single, installable .xpi file."

"Makes it easier for people with disabilities to view and navigate web content. A toolbar provides easy access to navigation, styling, and keyboard enhancement functionality. Developers can use the extension to check their structural markup from the brows

"Turn the web on its head with the Plain Old Webserver (POW), which adds a server to your browser."

"Firefox 2.0 uses Shift+Alt as the keystroke combination to invoke access keys. On the surface, this appears to be a great idea, as it avoids clashing with the shortcut keys used for the browser. Unfortunately, the new behaviour has been poorly implemente

"Open pages in Opera from Firefox and Mozilla context menus."

"A suite of tools and libraries that help make your life easier and your time more productive as a developer of AJAX and Mozilla applications. "

"Regularly-updated succinct compilations of the most important information on web pages. They are compact enough to fit in the space available to a bookmark label, provide more useful information about pages than static page titles, and are regularly upda

"An alternative Bugzilla client. It is a desktop application with interactive user interface and unique capabilities that are a valuable addition to the feature-rich web-based Bugzilla software."

"Replaces the behavior of Ctrl+Tab. Instead of directly changing tab it works some thing like Alt+Tab on windows."

"The X-Ray Firefox Extension let’s you see the tags on a page without viewing the sourcecode."

"Allows to choose if you want to view a PDF file inside the browser (as PDF or HTML), if you want to view it outside Firefox with your default or custom PDF reader, or if you want to download it!"

New debugging extension for Firefox.

"Resources for Mozilla's ongoing web browser accessibility work."

"Renders a text version of a web page similar to screen reader output. Helps developers find accessibility issues fast."

"Allows you to check the page you are browsing in the waybackmachine archive."

"I managed to use CSS to move the navigation <ul> from the end of the document (just above the footer) to the top of the document, and insert it precisely into the blue header <div>. That’s not clever in itself, but what is sweet is the fact that it cop

"Allows you to submit a form to a new tab or window."

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

"Adds HTML validation inside Firefox and Mozilla."

"Adds a menu and a toolbar with various web developer tools."

"Allows you to quickly move up a level in a site by pressing Alt + Up arrow."

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

"Adds context menu items for opening links and images in a new background tab (or foreground tab if your tabs normally open in the background), in a new background or foreground window, and in the current tab."

"Slogger is an extension for Mozilla Firefox which can create a customizable browser history, automatically store all pages you visit locally, log pages via various search providers, and more."

Newer version than on Moz Update

"Feb 14, 2005 -- Minimo ported Windows CE. Builds soon to be available."