Firefox is one of the most popular pieces of software out there.  With its functionality, speed, resource-efficiency, and customizable features, it is no wonder why this browser is still the head honcho in the category of Internet browsers.  Now five years old, Mozilla Firefox is still making waves in the Internet realm and it is likely to stay at the top of the pack for years to come.  One of the biggest factors contributing to Firefox's success is the seemingly endless list of extensions that are available for the flexible browser.  Firefox extensions are small software add-ons that expand the functionality of your browser.  Here are some of the best extensions that you can download for your Firefox setup:

AdBlock Plus

AdBlock Plus, commonly abbreviated as ABP, is perhaps the best and most comprehensive ad-blocking software for Firefox.  After installing this piece of software, all you have to do is subscribe to one of the many ad-blocking feeds that are shown to you when you install the extension.  You can then customize the ad-blocking settings to your personal preferences.  For example, if there are sites that you love and normally visit, then you may want to enable the ads for that site.

Greasemonkey

Greasemonkey is an extension that can take a little getting used to, but it is an extension that can change the way you use the Internet forever.  Greasemonkey is an extension that makes use of Java Scripts developed by programmers and script writers around the world.  Basically, these scripts customize the way that you view and use the Internet.  For example, you can get scripts that automatically buffer and load high-def versions of the YouTube videos you click on, or you can find scripts that allow for keyboard shortcuts or customized views in Facebook.  The options that Greasemonkey and its associated scripts have to offer are nearly limitless.

DownThemAll

DownThemAll is an exceptional download manager that works seamlessly with Firefox.  This extension allows you to make mass downloads, downloading all of the images and links from the current page, or filtering which ones to download.  DownThemAll also allows you to choose download directories, pause and resume downloads, customize download filters, customize file names for downloaded files, and more.

Tab Mix Plus

Another great Firefox extension is Tab Mix Plus, which turbo charges your tabbed browsing.  You can manage browser sessions, customize your tab controls, configure which links should be opened in new tabs, customize how your tabs behave when opening and closing tabs, and improve the overall look and feel of your tabbed browsing.  Be sure to download Tab Mix Plus to see the wide array of settings and options that it gives you when tab browsing in Firefox.