Hi, please see this : *https://support.mozilla.org/en-US/kb/mixed-content-blocking-firefox SHIELD ICON Tracking Protection One issue that seems more common lately is Firefox's Tracking Protection feature. When it is blocking content in a page, a shield icon will appear at the left end of the address bar next to the padlock icon. This article has more info on managing this feature: Tracking Protection *https://support.mozilla.org/en-US/kb/tracking-protection There is security software like Avast/AVG, Kaspersky, BitDefender and ESET that intercept secure connections and send their own certificate. *https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can *https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites *https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message *https://support.mozilla.org/en-US/kb/connection-untrusted-error-message *http://kb.mozillazine.org/Error_loading_websites *https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER If you are running any of the above this may be the issue. Please see their community forums for a work around. Please let us know if this solved your issue or if need further assistance.