Windows 7, Pro, 64-bit with the latest FF. I was using FF last night and all of my bookmark toolbar items disappeared. All the bookmarks disappeared out of my bookmarks folder also. I tried restoring from a backup with no luck. No errors, just no restored bookmarks.
So I tried resetting the Sync and replacing what was local with my Sync data. That did not work as well. Passwords synced, but not bookmarks.
I then tried uninstalling FF and having it remove my personal settings and did a fresh install. Reconnected to Sync. Again passwords synced, but no bookmarks.
Try to disconnect from Sync, quit Firefox, delete places.sqlite, restart Firefox, and re-set up Sync.
You can check for problems with the places.sqlite database file in the Firefox Profile Folder.
Do at least the bookmarks reappear after deleting places.sqlite with Firefox closed and restarting Firefox?
If that isn't the case then the most recent JSON backup may already been affected and you will have to restore the bookmarks from an older JSON backup in the bookmarkbackups folder.
You can also try to reset all data on the sync server by generating a new sync key while setting up sync.
Just the default ones. It creates a new places.sqlite when I fire up Firefox again. But does not Sync back in the bookmarks.
I tried restoring to several backups that were listed and nothing shows up.
I tried a Sync reset to replace all local data with Sync data. No luck. I'm going to try and setup a new Sync account, then link my tablet to it, and see if it pulls the bookmarks into the new account.
If you inspect the files in the bookmarkbackups folder, are there any of them that have a larger file size indicating that they (may) have your lost bookmarks stored in them?