I switched over from Chromium to Firefox mainly because of how Firefox Sync worked back then - in the way that it encrypted your sync data with a secret that Mozilla would never know. Now, with the new sync that just requires a tuple of email address and password, I wonder what - if anything - they use to encrypt the data so they cannot know what I store there (which is a strict requirement for me to even consider any kind of "cloud"-y offering). Given that email/password is used for authentication and authorization only (I'm pretty certain they'll have a routine for users to "reset" their password...), I'm worried they'd left out the one thing that made Firefox Sync usable for folk concerned with privacy...
I have the same general concerns you did but am less trusting, so I set up my own sync server. Check out Run your own Sync Server at mozilla.com.
If you're technically inclined, familiar with general LAMP server management and have a personal linux server handy, it isn't that hard. There's a time investment up front, but once I got it running, it's been working flawlessly across several platforms and multiple browser profiles. I hope they deprecate the old sync behavior but keep it in place for awhile to give time to migrate to the new sync behavior. It's been working so well it's been "set it (up) and forget it" since I first got it running, so it will take a little time just to remember the details so I can migrate to the new server code (assuming there is even a viable migration pathway).
That said, the old sync that required the code to add new browser instances (ie. Firefox on another device or OS) was a little cumbersome, so making that a little simpler would be welcome. That would make it easier for other members of the household to manage their own devices without requiring me to set up and manage it for them.