On my desktop PC I have a bookmark folder that contains all of the banking type urls I ever access. Although there are no passwords associated with the urls I still preferred the folder not be available on my laptop since, although not a great possibility, it would be a lot easier to steal the the LT than the DT. So I searched how to disable Sink: about:config>services.sinc.auto.connect>toggle to false. In my situation this really worked out great, because I deleted the said bookmark folder on the laptop but still have all the rest of the desktop bookmarks. I've essentially did the same on both PCs for and rebooted them so the service isn't even running. Of course if you haven't even opened a Sinc account this is all a moot point.