Here’s a testing tool for web applications which is easy to use and has a firefox plugin to record and play test runs

was developed by team of programmers and testers at ThoughtWorks. Selenium is a test tool for web applications. Selenium tests run directly in a browser, just as real users do. And they run in Internet Explorer, Mozilla and Firefox on Windows, Linux, and Macintosh. No other test tool covers such a wide array of platforms.

How does Selenium Work?
Selenium uses JavaScript and Iframes to embed a test automation engine in your browser. This technique should work with any JavaScript-enabled browser. Because different browsers handle JavaScript somewhat differently, we usually have to tweak the engine to support a wide range of browsers on Windows, Mac OS X and Linux.

Selenium IDE
Selenium is a test tool for web applications. Selenium tests run directly in a browser, just as real users do. And they run in Internet Explorer, Mozilla and Firefox on Windows, Linux, and Macintosh. No other test tool covers such a wide array of platforms.

Link: Selenium: Selenium
Link: Selenium: IDE (Firefox Plugin)