Selenium is a suite of tools used for browser automation testing. It was introduced in 2004 and is developed using JavaScript. Selenium has four main components: IDE, Remote Control, WebDriver and Grid. It is used to test web applications and can perform functional, regression and load testing. The Selenium IDE records user interactions in the Firefox browser and exports test cases to various languages. It has advantages like being open source and easy to use, but only supports the Firefox browser.