Ever since I've turned down IE for FF, I've never looked back. Firefox made a lot of new functionality that are included in many more browser, such as the add-on system. It enables user to add or remove functionalities from Firefox, making it the most customizable browser ever. There is however some downside. Memory usage. Firefox uses a lot of memory. Partly because it was founded on another old browser, partly because it had an exponential growth. However, never version tend to correct a lot of the memory leaks, and Firefox 3 uses a lot less memory than Firefox 2, which brought a lot of GUI changes.