Hi Lukas, From what I read, you backed up your data with Firefox Sync before a clean install of your OS. Now, after configuring your Sync account (with the previous Sync key and login credentials) you are not getting your bookmarks. Unfortunately, Firefox Sync is not a back up system and when you configured your account in the new installation this data (or "no data") took over the account, and probably the previous bookmarks where swiped out from the servers. In any case, you should confirm this scenario by navigating to: - Firefox -> Preferences -> Sync Tab and press Reset Sync under the Manage Account drop down menu. In the new window, select "Replace all data in this computer with the information in the Sync servers" and "Continue". Make sure that the browser is syncing by pressing "Sync Now" under "Tools". I hope this works. In the future, you should create a local back up of your bookmarks before performing any clean installation of Firefox.