Disable Safe Mode
Supported on: Firefox 60 or later, Firefox 60 ESR or later
Registry
HKLM
Software\Policies\Mozilla\Firefox HKCU
Software\Policies\Mozilla\Firefox Value name: DisableSafeMode
Enabled: DisableSafeMode = 1
Disabled: DisableSafeMode = 0
Description
If this policy is enabled, the user cannot restart the browser into safe mode. If this policy is disabled or not configured, safe mode is allowed.