Google loves firefox. Now if only Firefox Mac would go Cocoa ...
Official Google Blog: Get in sync refers to a new sync tool (slows FF startup) and the updated toolbar.
Update 6/8: An unexpected benefit -- this makes Firefox a much better RSS reader, and it can now be competitive with Bloglines. Every machine can have the same RSS feeds, and they're readily kept in sync. I don't know if it syncs read status though.
Update 7/10: Uh-oh. Once I got to 4 machines synching Firefox, and multiple simultaneous sessions, things went downhill. Performance became pretty darned miserable -- even on a fast machine I couldn't tolerate the time it took for FF to starup. My cookies seemed to get trashed. I'm setting the utility so that nothing is routinely synched, I'll sync on a periodic rather than regular basis.