QUIC (HTTP/3) can absolutely cause secure connection and SSL errors in Firefox. When firewalls or antivirus tools try to inspect encrypted traffic, they frequently break QUIC's unique encryption, triggering security alarms in Firefox
Just like the change you made in Chrome, you can force Firefox to bypass QUIC and use stable TCP connections instead:Open Firefox.Type about:config in the URL bar and press Enter.Click Accept the Risk and Continue.Search for the preference named network.http.http3.enable.Click the toggle button to switch it from true to false.Restart Firefox
I had a site blocking me, including grok.com
and found this as a solution.
after I relaunched both sites started working again.
It might be the issue you are experiencing.
end user issues suck, but not much I know to do about it.

