Selenium IDE is an integrated development environment for Selenium tests.
Operates as a Firefox add-on and PROVIDES an interface for developing and running individual test cases or ENTIRE test suites.
Selenium-IDE has a RECORDING feature, which will keep account of user actions as they are performed and store them as a reusable script to play back.
It also has a context MENU (right-click) integrated with the Firefox browser, which allows the user to pick from a list of assertions and verifications for the selected location.
Offers full editing of test cases.
Although it is a Firefox only add-on, tests created in it can also be run against other browsers by using Selenium-RC & specifying the name of the test suite on the command LINE.