Selenium supports most of the browsers but we should be noted IDE supports only Firefox and RC and Webdriver supports all most all browsers.
Selenium IDE plug-in available only for Firefox. We can record and run any web application.
Selenium RC supports all browsers but every time we need to run the RC server.
Selenium web driver supports all browsers and we no need to run RC server and it will invoke browsers directly and run successfully.
HtmlUnit driver is used to run in background and it won’t display UI. Advantage of html unit driver is very fast. This is nothing but headless browser testing.
Selenium webdriver supports all browsers and simply we need to download browser driver and we need to create an instance and we can work on it. As selenium web driver directly invokes the browser.
This is one of the biggest advantage from selenium it supports all browsers very smoothly.