Bad news on the Google Browser Sync / Firefox 3 front; Google has discontinued Google Browser Sync. At least, that's what a Google support person told a user; no official information on Google's product page or FAQ. It's not unexpected. This is the downside of Google Labs; a 20% project from a smart engineer can get released quickly but truly supporting a quality product takes a real team.
There are some alternatives. If all you want is bookmarks, there's lots of options. If you want cookies and passwords too the best bet seems to be Mozilla Weave. But it's an "experimental prototype," requires registration to install, and reports are that it's unstable.
I'm surprised how slow Google has been to support Firefox 3; there's not even a Toolbar version yet. Firefox is very valuable software to Google. There's no public data about how much money Google makes from Firefox, but there is information on what Google is paying for the privilege of being in the Firefox ecosystem. Google paid Mozilla over $50M for search ad traffic in 2006. And Google pays at least $1 / install for Firefox + Google Toolbar. They're not just giving that money away to be nice, they're paying to own the default search box. Nothing wrong with that, I just hope it translates into good support for the development of Firefox products.