About Fireware Web UI Session Expiration
To connect to Fireware Web UI you must authenticate to the Firebox. Management connections to Fireware Web UI expire after a period of inactivity. If your management connection expires, an error message appears, with a link to return to the login page. To reconnect to Fireware Web UI after your connection expires, you must log in again.
By default, your management session expires after 15 minutes of activity.
For a locally-managed Firebox, you can configure the Management Session timeout in the Authentication settings. For more information, see Set Global Firewall Authentication Values.