I recently did some operations on my Linux machine which reset my time/date settings, but I did not notice this at first. I quickly noticed while browsing that every site which I visited had an invalid security certificate as it was only valid for dates in the future. This is as one would expect. What is unexpected, is firefox did not present me with any certificate warnings for google.com. I checked the google certificate used to secure the connection, and it was indeed an invalid certificate due to my system's current time/date settings. I checked Preferences > Advanced > Cetificates > View Certificates > Servers and while there was a permanent 'www.google.com' certificate found in the 'USERTRUST Network' section, i did not see any exceptions which matched the google.com certificate I was presented. the mozilla directory had no cert_override file for me to examine Why does firefox neglect to tell me that google.com's security certificate is invalid, but tells me for every other website?