The old and new sync use the same backend but that may not help you here; if for instance; you were hoping to do directional merges. Note the old and new syncs use a different account, and that the new sync only offers a merge option. * [[How to update to the new Firefox Sync]] *[[How do I choose what types of information to sync on Firefox?]] Relying on sync alone to backup bookmarks could result in all devices having corrupt bookmarks listings. If you have bookmarks involved I personally strongly recommend you manually back them up before making any sync changes, and thereafter do so at regular intervals - say every 2nd week. Sync is not good at handling large changes and large merges of bookmarks, corruption or duplication could occur. * [[Restore bookmarks from backup or move them to another computer#w_manual-backup]]'''_manual-backup'''

Note there are plans to deprecate the old sync * https://blog.mozilla.org/services/2015/02/03/legacy-sync-migration/are