I still don't see it on Getfirefox.com but I did find it in one of its mirrors

I would think that this new version is also aout bug fixes, memory leaks and security updates same as 1.5.0.1 and 1.5.0.2, too bad that the What's new page is still in draft (May 2nd 11am GMT-5)

While hanging around in the mirror, it might be a good idea to give Bon Echo a test drive as well :D