http://selenium.openqa.org/

From the page: “Selenium is a test tool for web applications. Selenium tests run directly in a browser, just like real users do. It runs in Internet Explorer, Mozilla and Firefox on Windows, Linux, and Macintosh, Safari on the Mac. We have plans to target Safari on the iPhone in some months.

The quickest way to learn Selenium is via a Firefox plugin called Selenium IDE. It is quite compelling for developing tests in and quickly trying out Selenium before choosing Selenium for your project.”