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A browser extension is a small software module for customizing a web browser. Browsers typically allow a variety of extensions, including user interface modifications, ad blocking, and cookie management.[1]



Internet Explorer was the first major browser to support extensions, with the release of version 5 in 1999.[2] Firefox has supported extensions since its launch in 2004. Opera began supporting extensions in 2009, and both Google Chrome and Safari did so the following year. Microsoft Edge added extensions in 2016.[3]

API conformityEdit

In 2015, a community working group formed under the W3C to create a single standard application programming interface (API) for browser extensions.[4] While that goal is unlikely to be achieved,[5] the majority of browsers already use the same or very similar APIs due to the popularity of Google Chrome.

Chrome was the first browser with an extension API based solely on HTML, CSS, and JavaScript. Beta testing for this capability began in 2009,[6][7] and the following year Google opened the Chrome Web Store. As of June 2012, there were 750 million total installs of extensions and other content hosted on the store.[8] In the same year, Chrome overtook Internet Explorer as the world's most popular browser,[9] and its market share continued to grow, reaching 60% in 2018.[10]

Because of Chrome's success, Microsoft created a very similar extension API for its Edge browser, with the goal of making it easy for Chrome extension developers to port their work to Edge.[11] But after three years Edge still had a disappointingly small market share, so in December 2018 Microsoft announced that Edge is being rebuilt as a Chromium-based browser.[12][13] (Chromium is Google's open-source project that serves as the functional core of Chrome and many other browsers.) This remade Edge should have the same API as Chrome, which will enable users to install extensions directly from the Chrome Web Store.[13][14]

With its own market share in decline, Mozilla also decided to conform. In 2015, the organization announced that the long-standing XUL and XPCOM extension capabilities of Firefox would be replaced with a less-permissive API very similar to Chrome's.[15] This change was enacted in 2017 with the release of Firefox 57.[16][17] Firefox extensions are now largely compatible with their Chrome counterparts.[18]

Apple is the lone major exception to this trend. Its current API for Safari requires using the Xcode tool to create extensions.[19]

Unwanted behaviorEdit

Browser extensions typically have access to sensitive data, such as browsing history, and have the ability to alter some browser settings, add user interface items, or replace website content.[20][21] As a result, there have been instances of malware, so users need to be cautious about what extensions they install.[22][23][24][25]

There have also been cases of applications installing browser extensions in a sneaky manner, while making it hard for the user to uninstall the unwanted extension.[26]

Some Google Chrome extension developers have sold their extensions to third-parties who then incorporated adware.[27][28] In 2014, Google removed two such extensions from the Chrome Web Store after many users complained about unwanted pop-up ads.[29] The following year, Google acknowledged that about five percent of visits to its own websites had been altered by extensions with adware.[30][31][32]


  1. ^ "What are extensions?". MDN Web Docs. Retrieved 2019-08-05.
  2. ^ "Browser Extensions". Retrieved 2010-06-05.
  3. ^ Bright, Peter (18 March 2016). "Edge browser now has extensions in the latest Windows 10 preview". Ars Technica. Condé Nast.
  4. ^ "Browser Extension Community Group Charter — Browser Extension Community Group". Retrieved 2018-12-14.
  5. ^ "Re: One question from Florian Rivoal on 2017-07-29 ( from July 2017)". Retrieved 2018-12-14.
  6. ^ "Extensions Status: On the Runway, Getting Ready for Take-Off". Chromium Blog. Retrieved 2018-12-14.
  7. ^ "Extensions beta launched, with over 300 extensions!". Chromium Blog. Retrieved 2018-12-14.
  8. ^ Vikas SN (2012-06-29). "The Lowdown: Google I/O 2012 Day 2 – 310M Chrome Users, 425M Gmail & More". MediaNama. Retrieved 2013-06-14.
  9. ^ "Internet Explorer usage to plummet below 50 percent by mid-2012". 3 September 2011. Archived from the original on 20 November 2011. Retrieved 4 September 2011.
  10. ^ Statcounter. "Browser Market Share Worldwide | StatCounter Global Stats". Retrieved October 20, 2018.
  11. ^ "Porting an extension from Chrome to Microsoft Edge". Microsoft. Retrieved 30 December 2018.
  12. ^ "Microsoft Edge: Making the web better through more open source collaboration". Windows Experience Blog. 2018-12-06. Retrieved 2018-12-14.
  13. ^ a b Keizer, Gregg (2018-12-08). "With move to rebuild Edge atop Google's Chromium, Microsoft raises white flag in browser war". Computerworld. Retrieved 2018-12-14.
  14. ^ "r/Windows10 - Microsoft Edge: Making the web better through more open source collaboration". reddit. Retrieved 2018-12-15.
  15. ^ "The Future of Developing Firefox Add-ons". Mozilla Add-ons Blog. Retrieved 2018-12-15.
  16. ^ "Upcoming Changes in Compatibility Features". Mozilla Add-ons Blog. Retrieved 2018-12-15.
  17. ^ "How to enable legacy extensions in Firefox 57 - gHacks Tech News". Retrieved 2018-12-14.
  18. ^ "Porting a Google Chrome extension". Mozilla. Retrieved 30 December 2018.
  19. ^ "Building a Safari App Extension". Apple. Retrieved 10 February 2019.
  20. ^ "Protect User Privacy". Google Chrome Docs. Retrieved 2018-12-15.
  21. ^ "Add-on Policies". MDN Web Docs. Retrieved 2018-12-15.
  22. ^ "Security firm ICEBRG uncovers 4 malicious Chrome extensions - gHacks Tech News". Retrieved 2018-12-15.
  23. ^ "Google's bad track record of malicious Chrome extensions continues - gHacks Tech News". Retrieved 2018-12-15.
  24. ^ "Chrome Extension Devs Use Sneaky Landing Pages after Google Bans Inline Installs". BleepingComputer. Retrieved 2018-12-15.
  25. ^ "Google Chrome extensions with 500,000 downloads found to be malicious". Ars Technica. Retrieved 2018-12-30.
  26. ^ "PUP Criteria". Malwarebytes. Retrieved 13 February 2015.
  27. ^ "Adware vendors buy Chrome Extensions to send ad- and malware-filled updates". Ars Technica. Retrieved 20 January 2014.
  28. ^ Bruce Schneier (21 Jan 2014). "Adware Vendors Buy and Abuse Chrome Extensions".
  29. ^ Winkler, Rolfe. "Google Removes Two Chrome Extensions Amid Ad Uproar". Wall Street Journal. Retrieved 17 March 2014.
  30. ^ "Ad Injection at Scale: Assessing Deceptive Advertisement Modifications" (PDF). Archived from the original (PDF) on 2015-06-05.
  31. ^ "Superfish injects ads into 5 percent of all Google page views". PC World. IDG.
  32. ^ "Superfish injects ads in one in 25 Google page views". CIO. IDG.

External linksEdit

Extension API documentation from Google, Apple, Mozilla, Microsoft, Opera

Official extension stores for Chrome, Safari, Firefox, Edge, Opera