Add on security certificate issue is NOT fixed

I am in England&have not had a single issue till this week with firefox64b 79.0, it just kept saying we can’t make the connection as either you have no internet or the site certificate is expired.i tried old back ups old versions online but no Firefox whatever I did the only thing that worked for me was in to uninstall FF&dload the same copy off the Mozilla site but when installling again it asks if u’d like a bran new fresh version just like new,after pressing yes the 1st time I decided to go with no2nd time&just installed without any housekeeping as FF puts it&it came back on striaghtaway with all extensions&bookmarks working

Do you have any security software running at your computer, such as antivirus or AdGuard? It sound like some other app is sniffing your connection. Please try to disable them and restart Firefox to check if web browsing Is resume normal.