It is usually best to check out why the site is untrusted (Technical details) and if this is caused by a missing intermediate certificate then see if you can install this intermediate certificate from another source. You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates. *Click the link at the bottom of the error page: "I Understand the Risks" Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate". *Click the "View..." button and inspect the certificate and check who is the issuer. You can see more Details like intermediate certificates that are used in the Details pane. You can inspect the certificate chain via a site like this: *http://www.networking4all.com/en/support/tools/site+check/ Check the date and time in the clock on your computer: (double) click the clock icon on the Windows Taskbar. *https://support.mozilla.org/kb/Secure+Connection+Failed