Hi,
On new installation of Firefox we cannot connect to https://www.qlustar.com. The cause is missing intermediate certificate in server certificate chain response. By using
openssl s_client -connect www.qlustar.com:443
we can see very strange chain:
Certificate chain 0 s:CN = www.qlustar.com i:C = US, O = Let's Encrypt, CN = Let's Encrypt Authority X3 1 s:C = GB, ST = Greater Manchester, L = Salford, O = COMODO CA Limited, CN = COMODO RSA Domain Validation Secure Server CA i:C = GB, ST = Greater Manchester, L = Salford, O = COMODO CA Limited, CN = COMODO RSA Certification Authority 2 s:C = GB, ST = Greater Manchester, L = Salford, O = COMODO CA Limited, CN = COMODO RSA Certification Authority i:C = SE, O = AddTrust AB, OU = AddTrust External TTP Network, CN = AddTrust External CA Root
Let's Encrypt have different intermediate certificate.
Regards, Rolandas
P.S. It also caused problems with wget/curl to download files from your site.