Firefox Sync is a utility for syncing history, bookmarks, tabs and passwords between devices (computers) built in to Firefox 4 and later. How do I enable it?
I had that problem now it's solve the thing is that my account was sync on an older version of Firefox below version 29, to bypass that bug unlink all the Firefox with that account and the main browser where all your bookmmarks are or simply delete the account. And create a new account with a new email like an @gmail.com or @hotmail.com or anyone email and then sync your other computer with the new account created on the main computer or browser. Wait a few minutes then that should do.