I can't access this site from Firefox on PC

I always use Firefox on my pc but the last day or so I cannot access this forum or main site and get this error:

Secure Connection Failed
An error occurred during a connection to forums.forzamotorsport.net. Invalid OCSP signing certificate in OCSP response. Error code: SEC_ERROR_OCSP_INVALID_SIGNING_CERT
The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
Please contact the website owners to inform them of this problem.

I have the latest Firefox version 53.0.3 (32 bit)

I am posting this from my Chrome browser that I rarely use. Can you please fix this?

EDiT: Chrome also reports this site as “not secure” but shows it anyway. Point is this worked in FF some days ago so the problem must be at this site and not my browser. I think this sites “security certificate” has expired and the hosts are oblivious …sigh

Same for me, bypassed for the moment with this Is there anyway to fix a "Secure Connection Failed" (Error Code:sec_error_ocsp_unknown_cert)? | Firefox Support Forum | Mozilla Support

Seems to be working again now. I’ve noticed before that Turn10 have had certificate issues with Firefox on Android and PC. Usually it clears itself fairly quickly, but this has been a bit longer.

Yes I can now load this site again in FF but it’s still listed as “not secure” in the url both in Chrome and FF.
I think it’s embarrassing for them to mess such basic site maintenance up. Anyway here’s hoping it will keep working now …