What security software are you running? Windows home or pro?

kaspersky total security windows 10 pro v.10.0.19045

in the line where you type the url it says on all that the url is not secure, and it says that the connection is insecure, your connection is not private, others can see the information you send, under more info, under security it says among other things that I have not visited that website before which I have done many times before

it's only on my PC and only on firefox, I've tried deleting it completely also in the registry database and then trying to install an older one, it didn't work, it wanted a new one when starting firefox, under settings with firefox updates there are no new updates updated and it can't search for updates

I think I've found how, now it seems to be working again, I'll have to wait for a restart after removing the entire firewall and deleting the cache in Firefox. on https://helpdeskgeek.com/how-to-fix-the-pr_connect_reset_error-error-in-mozilla-firefox/

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution.

Thank you for contacting Mozilla Support.

now let's see what happens after reinstalling the firewall and rebooting

kaspersky total security windows 10 pro v.10.0.19045

Have a look. https://support.mozilla.org/en-US/questions/1444114

https://forum.kaspersky.com/topic/getting-pr_connect_reset_error-in-firefox-when-using-kaspersky-total-security-28248

Flood and Flood's wife on that forum helped me years ago with this issue.