I just noticed Ars Technica talking about it happening this week. Opera, Konqueror, and Safari, of course, had already passed the test. At the pace IE is going, it will pass the test after the web browser is considered obsolete.
It's nice to see that Mozilla finally got it going. It's interesting to me that the updated rendering engine makes use of vector graphics, which would explain how it deals with layered graphics better.
Firefox 3 has been in the works for a while. Think of it like Leopard. It is the next-gen, as-yet-unreleased software. Peoplel can play with Firefox 3 because it is open-source and everyone can watch it minute-by-minute. 10.5 is hidden in an underground vault protected by killer ferrets.