Can you connect a Windows PC and see if it can be disabled?
You might try this, factory reset, reload the FW file manually from the web site, you can even use the v2.12 beta as well if you want to. Factory reset once more then go directly in and see if you can disable DNS Relay using FF or Opera.
I should have some time this evening after work to check my Rev B and see what happens. I haven't had it online in a long time.