What do you mean?? Extending Firefox?
Firefox 1.0.7 ( http://www.mozilla.org/products/firefox/ ) is the next generation browser from the Mozilla project. Along with the current modern browser features like tabbed browsing and popup blocking capabilities, it also comes along with integrated searching and advanced keyboard navigation. But, what really can set your Firefox browsing experience apart are the extensions and themes that are available to make your browsing as efficient, informational and/or silly as you like.
In fact, you might spend more time customizing your browser than actually using it! Let’s get started…
Firefox “out of the box”
Knowing a few tricks with Firefox preferences can really make a difference without even downloading anything.
Find as you type: Using Find in Firefox is different from other browsers. It opens in the status bar at the bottom of the window so it doesn’t open a dialog box that covers the web page you are searching. If you go into the Tools > Options > Advanced dialog, you can check “Find as you type” This means the find function begins as soon as you start entering characters on the keyboard so you don’t have to use CTL+F to start the Find function
Set a group of pages as “Home”: We all know how to set a page as a homepage. But, if you have a set of pages that you like to start with as a homebase, set up the tabs with the pages that you like. Then, open Tools > Options > General and click the “Set Pages as Home” option.
Firefox Themes
Themes are customization of how Firefox looks. There are plenty of them out there. To find them:
Open Firefox >> Choose Tools > Themes and then click the “Get More Themes” link in the bottom right. A page will load in Firefox that has Themes listed to browse. Find one you like, right click the Install button, download the file (jar file) and drag it on top of the Firefox window and it is installed into Firefox and will be available the next time you start it up. <see example themes below>

Firefox with Brushed theme

Firefox with Azerty theme
Extensions
Extensions are small add-ons to Firefox that can make it more efficient or customize the information you see or just plain have fun. To install , right click and save the xpi file. Drag it on top of a Firefox window and it will install. To uninstall or see what you have: Choose Tools > Extensions.
Here are some to check out:
AdBlock – Once installed, use it to filter advertisements at their source-address.
ForecastFox – Get international weather forecasts from AccuWeather.com, and display it in any toolbar or statusbar.
FoxyTunes – Now you can control your favorite media player without ever leaving the browser
Scrapbook – helps you to save Web pages and easily manage collections.
Spoofstick – gives you the actual name of the server where you are visiting. Useful in avoiding spoofed sites for e-commerce or online banking.
StumbleUpon – StumbleUpon lets you “channelsurf” the best-reviewed sites on the web. It is a collaborative surfing tool for browsing, reviewing and sharing great sites with like-minded people. This helps you find interesting webpages you wouldn’t think to search for.
WebDeveloper – adds a menu and a toolbar to the browser with various web developer tools.
Helpful Resources
Firefox Extensions Directory – https://addons.mozilla.org/extensions/?application=firefox
Top 15 Firefox Extensions by PC Magazine – http://www.pcmag.com/article2/0,1895,1758849,00.asp
Best Firefox Extensions – http://db.rambleschmack.net/pc_tips/best_firefox_extensions