Computer Configuration > Administrative Templates > Firefox > Browser Data Backup
Both
HKLM\Software\Policies\Mozilla\Firefox\BrowserDataBackup
If this policy is enabled, browser profile data can be backed up when backup is supported on the platform. If this policy is disabled, browser profile data cannot be backed up. If this policy is not configured, backup availability follows the platform default. This policy cannot be used to enable backup on platforms or in configurations where backup is not otherwise supported.