According to the plan we published earlier for deprecating SHA-1, on January 1, 2016, Firefox 43 began rejecting new certificates signed with the SHA-1 digest algorithm.  For Firefox users with unfiltered access to the Internet, this change probably went unnoticed, & Continue reading

https://blog.mozilla.org/security/2016/01/06/man-in-the-middle-interfering-with-increased-security/