One of the things that makes Firefox appealing to so many Web users is the fact that it is extensible through the addition of custom add-ons. If you're a relative newcomer to the Firefox add-on scene, I would highly recommend Fashion Your Firefox, an interface on the Mozilla site that allows you to scroll through a list of popular add-ons, organized by category, select a few that look interesting, and install them with one click.
This may not come as a surprise, but we have a lot of Firefox users here at CommonPlaces. Of course, we test the sites we build in a wide range of browsers, but for general Web browsing, most of us call Firefox home. With this in mind, I sent an email out to the group hoping to get a small list of add-ons that the CommonPlaces team recommends. 42 add-ons later, I ended up with a list in serious need of trimming, and a browser window in jeopardy of being completely overtaken by toolbars.
So after much deliberation and testing, here is a condensed list of the Firefox add-ons that the CommonPlaces team couldn't live without. Thanks again to all the folks here who suggested their favorites.
Tab Mix Plus - Take control of your tabs in Firefox with Tab Mix Plus. This add-on gives you greater focus control, allows mutiple rows of tabs, has a handy duplicate tab feature that's accessed with a right mouse click, and offers a list of other helpful features. Sounds boring, but it will really improve your day-to-day experience with tabbed browsing.
IE Tab - This add-on won't change your life, but when you need it, it's a nice timesaver. Sometimes you want to see what a page looks like in Internet Explorer. Rather than copy the URL, open IE, and paste it in, simply right-click on the page and select "View Page in IE Tab". It's as easy as that.
StumbleUpon - Easily the most addiciting Firefox extension in existence, this little toolbar takes you on a rambling journey across the web, visiting a random, user-recommended page with each click of the Stumble button. When a Web technology becomes a verb ("I stumbled a really interesting article last night"), you know it's probably time to jump on the bandwagon.
FireShot - Hands down, this is the best way to do screen captures of the Web. You can capture the visible screen or the entire page (all that stuff you have to scroll to see), and you can even add notes to FireShot captures before you save them with the help of arrows, shapes, and text boxes. FireShot is a must, trust me!
Digg Firefox Extension - If you're a Digg user, especially a power user, this extension may be for you. It adds a Digg menu to your menu bar that quickly shows you how many diggs the current page has, provides a link to its Digg page, and if a page hasn't been dugg yet, provides a link to automatically submit it.
RSS Ticker - If you use RSS, I can't imagine passing up on this extension. The RSS Ticker will display your favorite feeds in a scrolling bar that can be placed at the top or bottom of the browser window. If you're addicted to RSS, this extension won't help you shake that addiction any time soon.
Find In Tabs - Ctrl+F (or Cmd+F, for my Mac friends) is a easy way to search the text in a given tab. But what if you wanted to search the text of all your open tabs at once? Download Find in Tabs, and that kind of search is a mouse click away. Search for a given keyword, and all instances of that keyword will be highlighted in all open tabs. Pretty cool, huh?