If you are trying to access your admin console remotely, you will need to enable secure admin.
Your admin user will need to have a password which you can set with asadmin change-admin-password if needed.
Once you have an admin user with a password, you can use asadmin enable-secure-admin to turn on secure admin. This means that you will need to go over https to get to your admin console.
After you enable secure admin, you will need to restart your domain for the change to take effect: asadmin restart-domain
The error you're getting suggests that Firefox can't reach port 4848, so make sure that the port is not blocked by any firewall.