Update: Mozilla Persona support has been removed. If you haven't associated an alternate login method with your account, please contact email@example.com.
The Mozilla Persona project has indicated that they are going to be shutting down in November 2016.
In preparation GPSLog Labs will no longer allow new accounts to be created using a Persona login.
If you login using Persona you will be advised to add alternative log in details to your account.
As with previous OpenID changes, if you have any difficulties (e.g. you see a new empty account after logging in), please contact firstname.lastname@example.org and I'll fix it up.