Well why was it blocked in IE and did firefox kick up a warning. Because of this DANG:
https://shaaaaaaaaaaaaa.com/check/www.discovery-design.de This server's certificate is not trusted - Signature algorithm SHA1withRSA WEAK
You have a TRUST issue and with that considered Qualys gives a poor T overall rating, else you would have reached B-Status.
As of January 1, 2016, no publicly trusted CA is allowed to issue a SHA-1 certificate. So any new certificate you get should automatically use a SHA-2 algorithm for its signature.
Additional Certificates (if supplied)
Certificates provided 1 (1146 bytes)
Chain issues Incomplete
Handshake Simulation
Android 2.3.7 No SNI 2 Incorrect certificate because this client doesn't support SNI
RSA 2048 (SHA1) | TLS 1.0 | TLS_RSA_WITH_AES_128_CBC_SHA
Handshake Simulation
Android 2.3.7 No SNI 2 Incorrect certificate because this client doesn't support SNI
IE 6 / XP No FS 1 No SNI 2 Server closed connection
IE 7 / Vista RSA 4096 (SHA1) TLS 1.0 TLS_RSA_WITH_AES_128_CBC_SHA No FS
IE 8 / XP No FS 1 No SNI 2 Incorrect certificate because this client doesn't support SNI
RSA 2048 (SHA1) | TLS 1.0 | TLS_RSA_WITH_3DES_EDE_CBC_SHA
Java 6u45 No SNI 2 Incorrect certificate because this client doesn't support SNI
Android 2.3.7 No SNI 2 Incorrect certificate because this client doesn't support SNI
Java 6u45 No SNI 2 Incorrect certificate because this client doesn't support SNI
Apple ATS 9 / iOS 9 R Client requires SHA2 certificate signatures
So you have a serious SSL Server Test Security Issue,
polonus