". . .We hit a couple of bumps with M6, our most recent release, but we’re working hard (and very late on a Friday) to bring back the great new features. In the meantime, we’ve restored the service to the prior release so that you can access your mail quickly and reliably without hitting any of those bumps. . ."
This means that firefox users won't get the new windows live mail experience and for now be satisfied with the classic hotmail interface.
Read more: Your mail is here, come and get it! (windows live mail blog)