Description: A browser extension is a computer program that extends the functionality of a web browser in some way. Depending on the browser and the version, the term may be distinct from similar terms such as plug-in or add-on. Extensions can be created through use of web technologies such as HTML, Java, and CSS. Browser extensions can also improve the user interface of the web browser without directly affecting viewable content of a web page. This improvement can be achieved through a variety of add ons such as toolbars and plug-ins. Microsoft Internet Explorer started supporting extensions from version 5 released in 1999. Mozilla Firefox has supported extensions since its launch in 2004. The Opera desktop web browser supported extensions from version 10 released in 2009. Google Chrome started supporting extensions from version 4 released in 2010. The Apple Safari web browser started supporting native extensions from version 5 released in 2010. You might want to use a browser extension for a few different reasons: o To integrate with other services you use. o To add additional features to your browser. o To modify websites as they appear on your computer â€” adding, removing, or modifying content. Extensions can do many other things. Theyâ€™re like any other piece of software, although browsers place some limits on what they can do. If you want to integrate your browser with a service or get an additional feature, thereâ€™s a good chance you can do it with a browser extension that already exists. How Secure Are They? Browser extensions are like any other piece of software. Malicious extensions could do bad things and even well-intentioned extensions could have bugs. As with any other type of software, from Windows desktop apps to iPhone apps, you should try to pick trustworthy extensions. Chrome gives you some idea of the permissions an extension requires when you install it, so you can see if the extension is only operating on a single website or has additional permissions. Firefox doesnâ€™t have a fine-grained permissions system, so extensions have access to the entire browser â€” and more. Internet Explorer has limited support for add-ons. Will They Slow Down Your Browser? You shouldnâ€™t overload your browser with extensions. Each extension is another piece of code running on your computer. Just as you wouldnâ€™t install a pile of applications you never use and let them run in the background on Windows, you should try to limit the number of extensions you use. On Chrome, many extensions run in their own process, adding another process to your system. Firefox runs all extensions in the same process, but many additional extensions can make Firefox even slower. Differences between Browsers: Chrome, Firefox, Internet Explorer: Different browsers have different extension systems. Firefox has the most powerful one. Many people use Firefox because of this â€” Firefox makes many advanced extensions possible that wouldnâ€™t be possible on other browsers. Because of its history, even extensions that would be possible in another browser may only be available for Firefox. Chrome also has a thriving extension ecosystem and thereâ€™s probably also a Chrome extension for most everything youâ€™d want to do. Chrome places more limits on its browser extensions so they canâ€™t be quite as powerful as they are in Firefox, but these limits allow Chrome to present permissions system and restrict extensions a bit more for security. Internet Explorer has a very small add-on ecosystem. Few add-ons are available, and most of the Internet Explorer add-ons in actual use are probably browser toolbars like the terrible Ask toolbar that were foisted on users through bundling with other software. If you want add-ons, Internet Explorer is not the browser to use. Safari and Opera also have extensions available, but their ecosystems are much smaller than Firefoxâ€™s and Chromeâ€™s. Extensions Arenâ€™t the Same as Plug-ins: Note that extensions, or add-ons, arenâ€™t the same as browser plug-ins. “Plug-ins” are things like Adobe Flash, Oracle Java, or Microsoft Silverlight. They allow websites to embed and render content â€” flash movies, PDFs, or Java applets. Where to Get Extensions? Chrome extensions are available from the Chrome Web Store, while Firefox extensions are available on Mozillaâ€™s Add-ons site. Microsoft hosts an Internet Explorer Add-on Gallery website, but the selection is extremely limited. Other browsers have their own sites. Smartphoneâ€™s and Tablets: Browser extensions havenâ€™t made the jump to mobile devices. Whether itâ€™s Safari on iOS, Chrome on Android, or Internet Explorer in Windows 8â€˛s Modern environment, none of these browsers has support for extensions. Youâ€™re probably better off using a dedicated app for whatever you want to do on mobile devices.