@DavidR, please try these 20 websites on your computer. To open them with a single command copy this to cmd.exe (for PowerShell you have to prepend an & before the line):
"C:\Program Files\Mozilla Firefox\firefox.exe" https://www.amazon.com/ https://www.youtube.com/ https://www.google.com/ https://www.apple.com/ https://www.usa.gov/ https://www.gov.uk/ https://www.ox.ac.uk/ https://www.nhs.uk/ https://www.nic.cz/ https://www.sport.cz/ https://www.super.cz/ https://www.dsl.sk/ https://www.cas.sk/ https://www.pravda.sk/ https://www.hs.fi/ https://www.telia.fi/ https://www.is.fi/ https://www.dmi.dk/ https://www.dbkk.dk/ https://www.krak.dk/
Check the Site information popup for each page. Please tell me, whether you have or haven’t seen the warning message.
For me some websites have the warning, some don’t have it. If I close all Firefox windows, and reopen these 20 websites, I usually get different results. I am curious, whether you experience the same.