How to disable `New Account Setup` wizard in Mozilla Thunderbird

I don't know of any way to disable the new account wizard but you could add an account with fake information and then set it to not automatically check the mail for that account. Thunderbird should stop bugging you about adding a new account and it shouldn't cause any problems (unless you click 'get mail' for that account).

Set Thunderbird to "offline mode", then go through the wizard. It won't attempt the tests and you can select "advanced" and it should drop you back to the accounts configuration page and continue setting up there.