There are some sites that are under active DDos attacks and/or been compromised and I have a few sites I go to that have that. Some have proxy accounts if google for them. Ok so with out knowing what sites but can try this : This looks like a problem with OCSP Stapling on the server because it works when OCSP Stapling is disabled in Firefox. https://en.wikipedia.org/wiki/OCSP_Stapling https://blog.mozilla.org/security/2013/07/29/ocsp-stapling-in-firefox/ You can temporarily disable OCSP Stapling : Type in the address bar about:config (press Enter) (promise to be careful, if asked) Type and look for the preference : security.ssl.enable_ocsp_stapling and set it's value to false It is best to reset this pref via the right-click context menu to true once you are done with this website. And : There is security software like Avast and Kaspersky and BitDefender and ESET that intercept secure connections and send their own certificate. http://www.ehow.com/how_11385212_troubleshoot-reset-connection-firefox.html https://support.mozilla.org/en-US/kb/server-not-found-connection-problem https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can 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 This Connection is Untrusted is sometimes caused because the computer system clock is wrong. Check the time / date / time zone settings. Give the above a try and see what happens. Please let us know if this solved your issue or if need further assistance.

Unfortunately non of this has solved the problem but as I'm able to access any sites that Firefox will not load on Safari perhaps I'll stick with Safari. Thanks anyway