Nearly all websites identified as "insecure" and cannot be accessed in latest "stable" version e.g. Google: Your connection is not secure The owner of www.google.co.uk has configured their web site improperly. To protect your information from being stolen, Firefox has not connected to this web site. This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox only connect to it securely. As a result, it is not possible to add an exception for this certificate. Learn more… Report errors like this to help Mozilla identify and block malicious sites www.google.co.uk uses an invalid security certificate. The certificate is not trusted because the issuer certificate is unknown. The server might not be sending the appropriate intermediate certificates. An additional root certificate may need to be imported. Error code: SEC_ERROR_UNKNOWN_ISSUER