Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
I don't get an error message. It is possible that there is a transparent proxy between you and StackExchange (with its root certificate installed on your machine). If this proxy is configured to sign the certificates using SHA-1, that would explain the error message, because the "Valid from" field on the certificate used on StackExchange is January 4, 2016, and Firefox doesn't accept certificates that are signed with SHA-1 with a "Valid from" date after January 1, 2016. Who is the issuer of the certificate you see?
