I replied to your second post here: https://support.mozilla.org/en-US/questions/980733

OOPs -Jeff beat me and the thread is is already locked. This sounds rather odd. I do now of another thread where someone reports additional bookmarks mysteriously appearing. I can understand some apparent problems; and possible causes, if any of this happens *You are using Firefox Sync (That may create bookmarks) *You try to delete Folders and the change does not take effect. (The database is locked or faulty) **Or the change does not survive a restart of the Computer (Sometimes software creates the prior state) *Any more details on exactly what happens ? <br />and whether any of the above seem to describe your problem ? * When does this occur exactly ? <br /> e.g.on Firefox Shutdown or Computer restarting for instance. *Do all your folders and contents get duplicated ?<br /> and does it occur every time Firefox is closed down (Or whatever the significant event.) Two initial suggestions # Check and attempt to repair the database using ''places maintenance''<br /> https://addons.mozilla.org/firefox/addon/places-maintenance/ <br />Also run the option from that add-on that produces a short report log, and paste it into your next reply. In fact please paste a log after the initial state,then after another couple of doublings; without you intervening to delete anything, #Try Firefox in Safemode <br />[[Troubleshoot Firefox issues using Safe Mode]]