This tutorial explains how to add extensions in Firefox using Selenium with Python. It covers the basics of Firefox extensions, including the WebExtensions API and XPI files. The tutorial also shows how to install extensions using the `install_addon` method of Selenium WebDriver, and how to use PyTest for testing. Additionally, it discusses the use of FirefoxProfile to load pre-loaded extensions in a Selenium-controlled Firefox instance. The goal is to provide developers with a comprehensive guide on how to add extensions in Firefox using Selenium with Python.