Please update to the current Firefox 37 release. *Help > About Firefox *https://support.mozilla.org/kb/update-firefox-latest-version. *https://support.mozilla.org/kb/Updating+Firefox The Firefox 36 version that you currently run is no longer supported with security updates. *It is important to update Firefox and add-ons to the latest version to get all security fixes. ---- 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 the intermediate certificates that are used in the Details tab.