It's probably being caused by an extension, since Firefox Sync has never caused problems like that with me, or you may have just accidentally copy-and-pasted the folders over and over somehow. Delete the duplicates then browse around Firefox a bit and use the add-ons, and check periodically to see if the folders have reappeared. If no folders appeared, you might've accidentally done something with your bookmarks before, and your problem is solved. If the duplicates have reappeared after you deleted them before, though, follow these steps:

1. Disable those add-ons.
2. Delete the duplicate folders.
3. Add a few bookmarks and browse on the web a little bit, restart Firefox, then check to see if the duplicate folders have appeared.

• If not...

1. Enable a single add-on.
2. Use it, performing various functions with it.
3. Check for duplicate folders after that.
4. Disable that add-on and enable the next one.
5. Repeat step 2 and go down until you've tried all add-ons.

• The add-on that was enabled when the duplicate folders were created (if this happens) is the problem.

You can check for problems with the places.sqlite database file in the Firefox profile folder.

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox
• https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file

• Places Maintenance: https://addons.mozilla.org/firefox/addon/places-maintenance/

If I were to make a guess I would say it's probably FEBE which I use to backup and/or syc settings that Firefox doesn't sync. Namely toolbar custom settings.

The way I keep my custom toolbars in sync on my 2 PCs is I use FEBE on 1 machine to backup all the data, then copy that data over to the other computers FEBE backup folder, then on that computer use FEBE to import prefs.js.

Do you know if there is a better way of syncing custom toolbars? Some kind of extension or configuration?

Thank you

You can copy your Firefox profile I guess, but that'll be kind of hard. To transfer your profile to another computer...

• Locate your profile.

1. Press the Windows logo key+R.
2. Type in %APPDATA%\Mozilla\Firefox\Profiles\ then click OK.
3. A window will open containing profile folders.

• Copy your profile.

1. To copy your profile, right click the folder with Default in its name, and click copy.
2. Paste the folder to a removable storage drive (like a USB stick).

• To move to the new computer.

1. Plug the drive into the other computer.

• Completely close Firefox on that computer.
• Use the Firefox Profile Manager to create a new profile in your desired location, then exit the Profile Manager.
• Locate the backed up profile folder on your hard drive or backup medium (e.g., your USB-stick).
• Open the profile folder backup (e.g., the xxxxxxxx.default backup).
• Copy the entire contents of the profile folder backup, such as the mimeTypes.rdf file, prefs.js file, bookmarkbackups folder, etc.
• Locate and open the new original profile folder of that computer.

1. Press the Windows logo key+R.
2. Type in %APPDATA%\Mozilla\Firefox\Profiles\ then click OK.
3. A window will open containing profile folders.

• Paste the contents of the backed up profile folder into the new profile folder, overwriting existing files of the same name.
• Start Firefox.

(I can show you in a video if you want. It sounds harder than it is) Note: Doing this will overwrite any settings, bookmarks, etc specific to Firefox of that computer!