A Browser Extension or Add-on are programs that can be installed into a web browser that extend the functionality of the browser. For the most part, extensions and add-ons are beneficial to a browser as they can be used to increase the the browser's performance and add additional, and in many times needed, functionality. This could include optimizing the browser's memory so it runs better, blocking ads, or saving open tabs to be used later. On the other hand, there are also unwanted extensions and add-ons that produce behavior that is only designed to generate revenue for the developer.
Unfortunately, unwanted extensions and add-ons are becoming more and more popular due to the legal limbo that these types of programs currently reside in. As most unwanted extensions and add-ons are installed manually or through programs that show opt in choices, even if they are confusing, they are currently considered legal. That does not change the fact that these types of extensions provide no apparent benefit to the user and only are designed to generate revenue for the developer.
Currently, unwanted extensions and add-ons exhibit unwanted behavior that includes:
While the vast majority of extensions and add-ons must be installed manually, many unwanted extensions are also being installed through adware bundles. For the most part, these bundles will bury the information about an unwanted extension in an end user license agreements (EULA) or in confusing installation screens. Therefore, it is important that everyone should read the license terms when installing a free program from the Internet.
It should also be noted that when referring to extensions most people think of Google Chrome and when referring to add-ons they think of Firefox. The word extension is used interchangeably, though, so it can become confusing. Ultimately, they both perform the same task; to add functionality, whether good or bad, to a web browser.