Browser plugin

A browser extension is a plug-in that extends the functionality of a web browser in some way. Some extensions are authored using web technologies such as HTML, JavaScript, and CSS. Browser extensions can change the user interface of the web browser without directly affecting viewable content of a web page; for example, by adding a "toolbar."

Internet Explorer started supporting extensions from version 5 released in 1999.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 Safari web browser started supporting native extensions from version 5 released in 2010. Microsoft Edge started supporting limited extensions in March 2016.

The syntax for extensions may be quite different from browser to browser, or at least different enough that an extension working on one browser does not work on another. As for search engine tools, an attempt to bypass this problem is the multi-tag strategy proposed by the project Mycroft, a database of search engine addons working on different browsers.

Many browsers have an online "store" that allow users to find extensions and see lists of popular extensions. For example, Google Chrome, Firefox, and Safari. all provide such stores, together with unofficial stores.

Browser extensions are most commonly used for improving security, accessibility, blocking advertisements, and generally improving a browser's user interface and adding various other features to make browsing the internet more easy and pleasant. There are often many available extensions that serve similar purposes, from which a user can choose.

A browser toolbar is a toolbar that resides within a browser's window. All major web browsers provide support to browser toolbar development as a way to extend the browser's UI and functionality. Browser toolbars are considered to be a particular kind of browser extension that presents a toolbar. Browser toolbars are specific to each browser, which means that a toolbar working on a browser does not work on another one.

In addition to toolbars, browser extensions add specific abilities into browsers using application programming interfaces (APIs) allowing third parties to create plug-ins that interact with the browser. The original API was NPAPI, but subsequently Google introduced the PPAPI interface in Chrome.

...
Wikipedia