What is the full message?

There is security software like Avast, Kaspersky, 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/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://www.bing.com/search?q=web+site+access+denied

https://support.mozilla.org/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

This Connection is Untrusted is sometimes caused because the computer system clock is wrong. Check the time / date / time zone settings.

Thank you for your reply.

The full message is as following (translation from German as I was trying to visit the link http://www.ehow.com/how_11385212_troubleshoot-reset-connection-firefox.html):

"Error: Connation Error

Firefox cannot set up connection to the Server under www.ehow.com

The website may be temperarily not accessible. Please try again later.

If you cannot access the other websites as well, please check the network/internet connection.

If your computer or network is proctected from a firewall or proxy, please be sure, that firefox is allowed to access the internet."

I have spent the last few days, trying pretty much every possible solution being offered by the mozila help site, but none of them works so far, and the problem still occured even as I used the safe-mode.

The links I posted should help.