The initial release of the Website Testing project occurred during the development cycle of Firefox 3 but was only run by a couple of employees and contributors. As a result we did not receive much feedback and that hasn't helped us to to get a better view of how Firefox behaves on different banking, financial, or shopping sites. That issue had to be addressed.
With the new web based version we want to give website testing a new look and broaden the interest in having people from all around the world help in this effort. Everyone who is interested is welcome to check if his/her major websites, primarily those which need accounts to be functional, are working as expected. It is free to join and you can help to make Firefox better than it already is!