It looks like the SSL certificate currently being served has been revoked. For me, it's blocked in FF, but allowed in Chrome.
Does anyone know if this is related to them moving php.net to new servers after the earlier malware attack?
Actually, after further review, it looks like the issue is with a revoked intermediate certificate that is sent along in the chain. It still causes issues in FF, but at least it's not directly with the PHP.net certificate.