Obviously this is only one anecdote so take it with a grain of salt but my experience with Firefox Sync was abysmal. I had it corrupt my bookmarks db twice in a year of using it. Fixing it required digging into my profile folder on Windows and manually deleting the db file while also disabling sync. Otherwise it would just redownload the corrupted db. It was bad to the point where I couldn’t even make new bookmarks with the corrupted file.

Anyway, it really burned me on FF since. It’s probably fixed now (or at least I hope it is) and I want to go back but given the lack of priority put on FF by Mozilla I’m just nervous to make the change again.