Sync isn't intended to be used a backup medium for a solitary device. Mozilla created it to synchronize Firefox data across multiple installations. For reinstalling the operating system, backing up the entire Profile is advised; then copy the files that are in the backup into the newly created Profile in the fresh Firefox installation. --------------- The biggest problem that Firefox Sync users run into using Sync as a backup medium ''(rather than as intended)'' is if they set a new account password their data their data is wiped from the Sync server; so without having a 2nd device using Sync their data can't be put back "into Sync". The Firefox Account password is used to create the encryption algorithm for their Firefox data while it is off of their devices, change the account password and their data on the Sync server is rendered useless; so that data is deleted. That scheme also allows the user to clear data from the Sync server should the need for a fresh start arise. ''Ten years ago I had corrupt data issues with Sync, and I almost ran out of email addresses when creating additional new accounts to get to the bottom of my problem. That was with the 1st version of Sync before it became built into Firefox; the Weave extension which was used to develop Sync. The 1.1 version with a "recovery code" feature came about 3 months prior to Sync being in to Firefox 4.0; that "code" provided the needed "data clear" feature and provided slightly better encryption for Firefox user data.''