Browser Extensions are small computer programs that extend the functionality of web browsers.  Extensions are used for everything from the practical (such as changing the user-interface of popular websites to improve them) to the frivolous (replacing all embedded video with Rick Roll videos).

All the major web browsers have browser-specific online databases to showcase user-submitted extensions: the Google Chrome Web Store, Mozilla’s Firefox Add-ons repository, Opera’s Add-ons and Themes gallery, and Microsoft’s Internet Explorer Gallery.

For more information about discovering, managing, and enjoying extensions, check out the following How-To Geek articles:

•  How to Install Extensions From Outside the Chrome Web Store
• Convert Bookmarklets Into Chrome Extensions
• Replace Your Favorite Abandoned Extensions in Firefox with This List of Alternatives
• Access the Options for Your Favorite Extensions Easier in Firefox
• Beginner Guide for Greasemonkey Scripts in Google Chrome