WebExtensions

A browser extension is a plug-in that extends the functionality of a web browser. Some extensions are authored using web technologies such as HTML, JavaScript, and CSS. Others are developed using machine code and application programming interfaces (APIs) provided by web browsers, such as NPAPI and PPAPI. 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 browser 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. Safari 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 allows users to find extensions and see lists of popular extensions. Google Chrome, Firefox, Opera and Safari all provide such stores.

Browser extensions are used for improving a browser's user interface, security or accessibility, blocking advertisements, and various other features to make browsing the internet easier and more pleasant. There are many types of extensions that can be used to control various aspects of browsing privacy and mitigate threats. For instance, they may prevent third parties from tracking the user's movements, block ads and scripts, or enforce good habits.

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