I read yesterday that Google has decided not to port Browser Sync to Firefox 3 and to finish supporting it at the end of this year. I’m very sorry to hear this as I really have come to rely on it.
I’ve installed Foxmarks in preparation but, although it does a good job of synchronising bookmarks, it doesn’t handle history, cookies and passwords. I guess I’m going to have to knock something up myself when I have time. It shouldn’t be that hard to do.