I choose to also install an older version of Firefox (43.0). On that version I get a The page you are trying to view cannot be shown because the authenticity of the received data could not be verified error.

Does the error page have an Advanced button which reveals more technical information about why Firefox can't verify the certificate?

By the way, Firefox 133 can still use TLS 1.0 and 1.1 if you modify some hidden settings. Of course, you wouldn't want to use these outside your LAN for any sensitive work, but here's how:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.

(2) In the search box in the page, type or paste tls.version and pause while the list is filtered

(3) Double-click the security.tls.version.min preference to display an editing field, and change the value to the highest value that works with your target system, then press Enter or click the blue check mark button to save the change.

• 3 = TLS 1.2
• 2 = TLS 1.1
• 1 = TLS 1.0