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

I have not tried Tor recently. Is that what you posted this question from? The old forum software we have recently rolled back to picks it up as Windows 10.

I probably have installs of Mint and if I remember correctly they normally have Firefox as the default browser. But although they will be available for all users Tor or a Mozilla build of Firefox are presumably custom installs.

I suggest you check your network settings for Firefox. I also suggest you check the locations of the Firefox| Tor profiles. It is generally s bad idea to share profiles - inadvertently or otherwise - with different Firefox installs. Keying in about:support or about:profiles may help you work out what profiles are in use for each install. CVCC

One install to many profiles is fine. Avoid one profile yo multiple installs. These helping article are aimed at Windows users but may be worth looking at as you probably have specialised security & privacy software

• Fix problems connecting to websites after updating Firefox
• Websites show a spinning wheel and never finish loading