Browser extensions are add-ons that allow you to customize your internet browser so that it functions better, so it does not feel like it limits you. It is like customizing a new car by adding accessories to it, or adding color changing lights.
Browser extensions allow you to do more than just visit websites, giving you control over how certain pieces of information appear on a page. They vary in what they can do and their purpose, so be sure you know what exactly the features of the one you use.
Similar to how JavaScript can leverage its own set of APIs and make data calls, extensions can do this as well. They are developed to work on a web page in a similar way to the JavaScript files that exist on the website.
Developers often use browser extensions to add new functionality and remove unwanted elements on websites - such as ads, auto-play features in regards to online videos