Symantec CA has been found to have issued a large number of problematic certificates in the past few years. Chrome 70 will stop trusting Symantec’s old certificate. The beta version of Chrome Canary has stopped trusting Symantec certificates.
Now, Mozilla has announced that its beta version, Firefox Nightly 63, will stop trusting Symantec-issued certificates, and users who visit Symantec-certified sites will see a warning message. Mozilla recommends that site owners replace old certificates as soon as possible.