RTL did probably mess up there content hosting, the only way I see is to add an exeption for cdn.digitaltext.rtl.de.
- Websites prove their identity via certificates. Firefox does not trust this site because it uses a certificate that is not valid for cdn.digitaltext.rtl.de. The certificate is only valid for the following names: a248.e.akamai.net, *.akamaized.net, *.akamaihd-staging.net, *.akamaihd.net, *.akamaized-staging.net
- Error code: SSL_ERROR_BAD_CERT_DOMAIN