SHA1 certificates for secure SSL/TLS communications are deprecated due to known computational vulnerabilities. To ensure secure communications, a forced deprecation sounds reasonable (i.e. refuse to connect to these). That has the side effect that it will lock out many users who are unable to use stronger hashes such as SHA256. However, if a fallback to SHA1 is provided (as Facebook is proposing), everyone will be vulnerable to SHA1 downgrade man-in-the-middle attacks.
What to do?
(Score: 0) by Anonymous Coward on Friday December 11 2015, @06:13PM
I have an Ancient GnuSense Laptop that I have not gotten around to upgrading yet. I get similar mysterious failure. Sometimes websites will work for a while, then suddenly refuse to (looking at you ixquick).
I strongly suspect lack of support for newer hash algorithms is the problem.