I began receiving the following message about 3 days ago - PR_CONNECT_RESET_ERROR. As I was browsing the forum I came across a suggestion to disable add-ons and restart Firefox in safe mode. When I did that I could now connect to the website I wanted. I then re-stared Firefox multiple times disabling the Add-ons one at a time.

In my case the culprit is "DuckDuckGo" priviacy and security add-on. When I disabled that and re-started Firefox I was able to connect. WhoYah!!!