I have login problem that you describe, but offer no solution

The browser doesn't know which service or appliance is interfering with the connection, just it's very likely the culprit for not succeeding. Unless it's an enterprise IT setup you probably know which Norton, Eset, Kaspersky, Avast etc. product you have installed, and could liaise with their support how to turn that feature off (or if there's an update necessary from their side).

I keep getting the same error message intermittently:==>

      "Your connection may not be private An app or service may see your encrypted traffic from this site."

Usually accompanied by a loss of internet (browser) connection: Network Diagnostic fails to reveal problem, may run for excessive length of time. However, System Analysis and/or Status always show "connected to Internet" -

       WiFi and Internet/Ethernet -OK

Sometimes corrected by a Refresh or Ctrl R Otherwise a Reboot / Restart is the only solution

There's no problem with connection to internet. There's something listening in to your HTTPS content, and if that third party scanning thing fails (as its various HTTP/3, QUICK, happy eyeballs capabilities, implementation and libraries are usually behind what browsers need to connect out efficiently), that scanning software can eventually stall some types of connections. To the extent Firefox doesn't see anything responding to its requests.

Thanks all!