I installed Tor on my Windows 7 PC in parrallel to Firefox. Both products can be run at the same time without any problem. My intention is to uninstall Firefox once I am Sure that Tor can be used without any problem. In order to reach this goal I decided first to Sync the Tor browser with the existing Firefox. Unfortunately although my Sync UserID and Password are accepted and with the message telling me that the Tor browser sync would start shortly nothing happens except an error message that I translate from the French to English: "Sync met an error during the synchronisation: Unknown error. Sync will try the operation again automatically."
That error seems to be a permanent error because I still have it after 1 hour or so.