A browser extension is a

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

module for customizing a

web browser A web browser, often shortened to browser, is an application for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's scr ...

. Browsers typically allow users to install a variety of extensions, including

user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine fro ...

modifications,

cookie A cookie is a sweet biscuit with high sugar and fat content. Cookie dough is softer than that used for other types of biscuit, and they are cooked longer at lower temperatures. The dough typically contains flour, sugar, egg, and some type of ...

management,

ad blocking Ad blocking (or ad filtering) is a software capability for blocking or altering online advertising in a History of the web browser, web browser, an Application software, application or a network. This may be done using browser extensions or othe ...

, and the custom scripting and styling of

web page A web page (or webpage) is a World Wide Web, Web document that is accessed in a web browser. A website typically consists of many web pages hyperlink, linked together under a common domain name. The term "web page" is therefore a metaphor of pap ...

s. Browser plug-ins are a different type of module and no longer supported by the major browsers. One difference is that extensions are distributed as

source code In computing, source code, or simply code or source, is a plain text computer program written in a programming language. A programmer writes the human readable source code to control the behavior of a computer. Since a computer, at base, only ...

, while plug-ins are

executable In computer science, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instruction (computer science), in ...

s (i.e.

object code In computing, object code or object module is the product of an assembler or compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' ...

). The most popular browser,

Google Chrome Google Chrome is a web browser developed by Google. It was first released in 2008 for Microsoft Windows, built with free software components from Apple WebKit and Mozilla Firefox. Versions were later released for Linux, macOS, iOS, iPadOS, an ...

, has over 100,000 extensions available but stopped supporting plug-ins in 2020.

History

Internet Explorer Internet Explorer (formerly Microsoft Internet Explorer and Windows Internet Explorer, commonly abbreviated as IE or MSIE) is a deprecation, retired series of graphical user interface, graphical web browsers developed by Microsoft that were u ...

was the first major browser to support extensions, with the release of version 4 in 1997.

Firefox Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements curr ...

has supported extensions since its launch in 2004.

Opera Opera is a form of History of theatre#European theatre, Western theatre in which music is a fundamental component and dramatic roles are taken by Singing, singers. Such a "work" (the literal translation of the Italian word "opera") is typically ...

and Chrome began supporting extensions in 2009, and

Safari A safari (; originally ) is an overland journey to observe wildlife, wild animals, especially in East Africa. The so-called big five game, "Big Five" game animals of Africa – lion, African leopard, leopard, rhinoceros, African elephant, elep ...

did so the following year.

Microsoft Edge Microsoft Edge is a Proprietary Software, proprietary cross-platform software, cross-platform web browser created by Microsoft and based on the Chromium (web browser), Chromium open-source project, superseding Edge Legacy. In Windows 11, Edge ...

added extension support in 2016.

API conformity

In 2015, a community group formed under the

W3C The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working together in ...

to create a single standard

application programming interface An application programming interface (API) is a connection between computers or between computer programs. It is a type of software Interface (computing), interface, offering a service to other pieces of software. A document or standard that des ...

(API) for browser extensions. While this particular work did not reach fruition, every major browser now has the same or very similar API due to the popularity of

. Chrome was the first browser with an extension API based solely on

HTML Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It defines the content and structure of web content. It is often assisted by technologies such as Cascading Style Sheets ( ...

, CSS, and

JavaScript JavaScript (), often abbreviated as JS, is a programming language and core technology of the World Wide Web, alongside HTML and CSS. Ninety-nine percent of websites use JavaScript on the client side for webpage behavior. Web browsers have ...

. Beta testing for this capability began in 2009, and the following year

Google Google LLC (, ) is an American multinational corporation and technology company focusing on online advertising, search engine technology, cloud computing, computer software, quantum computing, e-commerce, consumer electronics, and artificial ...

opened the

Chrome Web Store Web Store is Google's online store for its Chrome web browser. As of 2024, Chrome Web Store hosts about 138,000 extensions and 33,000 themes. History Chrome Web Store was publicly unveiled in December 2010, and was opened on February 11, 20 ...

. As of June 2012, there were 750 million total installations of extensions and other content hosted on the store. In the same year, Chrome overtook

as the world's most popular browser, and its usage share reached 60% in 2018. Because of Chrome's success,

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

created a very similar extension API for its

Edge Edge or EDGE may refer to: Technology Computing * Edge computing, a network load-balancing system * Edge device, an entry point to a computer network * Adobe Edge, a graphical development application * Microsoft Edge, a web browser developed by ...

browser, with the goal of making it easy for Chrome extension developers to port their work to Edge. But after three years Edge still had a disappointingly small market share, so Microsoft rebuilt it as a

Chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

-based browser. (Chromium is Google's open-source project that serves as the functional core of Chrome and many other browsers.) Now that Edge has the same API as Chrome, extensions can be installed directly from the Chrome Web Store. In 2015,

Mozilla Mozilla is a free software community founded in 1998 by members of Netscape. The Mozilla community uses, develops, publishes and supports Mozilla products, thereby promoting free software and open standards. The community is supported institution ...

announced that the long-standing XUL and

XPCOM Cross Platform Component Object Model (XPCOM) is a cross-platform component model from Mozilla. It is similar to Component Object Model (COM), Common Object Request Broker Architecture (CORBA) and system object model (SOM). It features multiple ...

extension capabilities of

would be replaced with a less-permissive API very similar to Chrome's. This change was enacted in 2017. Firefox extensions are now largely compatible with their Chrome counterparts.

Apple An apple is a round, edible fruit produced by an apple tree (''Malus'' spp.). Fruit trees of the orchard or domestic apple (''Malus domestica''), the most widely grown in the genus, are agriculture, cultivated worldwide. The tree originated ...

was the last major exception to this trend, but support for extensions conforming to the Chrome API was added to

for

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

in 2020. Extensions were later enabled in the

iOS Ios, Io or Nio (, ; ; locally Nios, Νιός) is a Greek island in the Cyclades group in the Aegean Sea. Ios is a hilly island with cliffs down to the sea on most sides. It is situated halfway between Naxos and Santorini. It is about long an ...

version for the first time. In 2021, these browser vendors formed a new W3C community group, called WebExtensions, to "specify a model, permissions, and a common core of APIs". However, Google joined this during its overhaul of Chrome's extension API, known as

Manifest V3 Google Chrome is a web browser developed by Google. It was first released in 2008 for Microsoft Windows, built with free software components from Apple WebKit and Mozilla Firefox. Versions were later released for Linux, macOS, iOS, iPadOS, an ...

, which greatly reduces the capability of

ad blockers Ad blocking (or ad filtering) is a software capability for blocking or altering online advertising in a web browser, an application or a network. This may be done using browser extensions or other methods or browsers with inside blocking. Hist ...

and

privacy Privacy (, ) is the ability of an individual or group to seclude themselves or information about themselves, and thereby express themselves selectively. The domain of privacy partially overlaps with security, which can include the concepts of a ...

-related extensions. Thus the WebExtensions group is viewed by some extension developers as nothing more than Google imposing its Manifest V3 design.

Unwanted behavior

Browser extensions typically have access to sensitive data, such as

browsing history Web browsing history refers to the list of web pages a user has visited, as well as associated metadata such as page title and time of visit. It is usually stored locally by web browsers in order to provide the user with a history list to go back ...

, and they have the ability to alter some browser settings, add user interface items, or replace website content. As a result, there have been instances of

malware Malware (a portmanteau of ''malicious software'')Tahir, R. (2018)A study on malware and malware detection techniques . ''International Journal of Education and Management Engineering'', ''8''(2), 20. is any software intentionally designed to caus ...

, so users need to be cautious about what extensions they install. There have also been cases of

applications Application may refer to: Mathematics and computing * Application software, computer software designed to help the user to perform specific tasks ** Application layer, an abstraction layer that specifies protocols and interface methods used in a ...

installing browser extensions without the user's knowledge, making it hard for the user to uninstall the unwanted extension. Some

extension developers have sold their extensions to third-parties who then incorporated

adware Adware, often called advertising-supported software by its developers, is software that generates revenue by automatically displaying Online advertising, online advertisements in the user interface or on a screen presented during the installatio ...

. In 2014,

removed two such extensions from the

after many users complained about unwanted pop-up ads. The following year, Google acknowledged that about five percent of visits to its own websites had been altered by extensions with adware.

References

External links

*Extension API documentation fro
GoogleAppleMozillaMicrosoftOpera
*Official extension stores fo
ChromeFirefoxEdgeOpera
{{Web interfaces Software add-ons Web browsers