What Is a Browser Extension? with example 

A browser extension is a plugin for an internet browser that adds additional functionalities and features to it that were not originally there or developed by the developers of the browser itself. 

Extensions have the ability to modify the user interface and add Web service functionality to a browser.

You can think of a browser extension as a small unit of software, oftentimes referred to as a plug, 

that can perform various controls as well as filters to change the way a user can visit a web page or view information from a specific web service. 

It can take advantage of similar application program interfaces or APIs that JavaScript can on a web page, and extensions even have access to their own set of APIs.

Alongside being used to enhance the functionality of a website, browser extensions can also be used to remove unwanted elements,

 such as pop-up advertisements and auto-play features in regard to online videos.