Invalid https certificate https://maps.stamen.com/

[jjimenezshaw]

If I try to visit https://maps.stamen.com/toner (see the https), Firefox returns this error
SSL_ERROR_BAD_CERT_DOMAIN
and does not allow me to visit the page
Chrome says NET::ERR_CERT_COMMON_NAME_INVALID

Existing the page in https, it is confusing that it has an invalid certificate.

However https://stamen.com/ does work fine.