Your issue seems a bit more complicated and requires more investigation. We're currently looking into it and we'll get back to you with more details ASAP. Please understand that escalations can take up to 72 hours for a response, but no longer.

SHA 256? More information on this type of encryption:

• https://blog.mozilla.org/security/201.../phasing-out-certificates-with-sha-1-based-signature-algorithms/

The proposed maintenance:

• Mozilla governance Security Group

If we cannot investigate there is a mailing list https://www.mozilla.org/en-US/about/f.../#dev-security-policy

I can not even access chancerygroupplc.co.uk from developer edition.

Running a check on the site using

• https://www.ssllabs.com/ssltest/analyze.html?d=chancerygroupplc.co.uk

I see that it is using RC4 which is broken since 2013 See for instance

• https://blog.mozilla.org/security/2013/11/12/navigating-tls/
  • https://wiki.mozilla.org/Security/Server_Side_TLS#RC4_weaknesses
• https://community.qualys.com/blogs/securitylabs/2013/03/19/rc4-in-tls-is-broken-now-what?
• https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2013-2566

The site does work using Firefox Release, IE & Chrome. I discover the site appears to be used for secure collection of debts !!

P.S. I note it is now a standards RFC https://tools.ietf.org/html/rfc7465

February 2015
Prohibiting RC4 Cipher Suites

Abstract

  This document requires that Transport Layer Security (TLS) clients
  and servers never negotiate the use of RC4 cipher suites when they
  establish connections.  This applies to all TLS versions.  This
  document updates RFCs 5246, 4346, and 2246.