This website only works via HTTP and not via secure HTTPS. If you use https://www.rinconbeach.com/ or Firefox forces https:// then it fails with a domain error and it you override this error then you get the Cloudflare 404 error page. So you need to open http://www.rinconbeach.com/ Firefox insisted for some reason in using HTTPS and with a lot of effort I was able to identify this as caused by "network.trr.mode = 2" (TRR first). Setting network.trr.mode to 0 or 1 allowed me to open http://www.rinconbeach.com/ *about:config => network.trr.mode = 0 (off) or 1 (parallel/fastest) You can open the <b>about:config</b> page via the location/address bar. You can click the button to "Accept the Risk and Continue". *https://support.mozilla.org/en-US/kb/about-config-editor-firefox

If you have enabled HTTPS-Only mode then you need to create an 'Off' exception. *https://support.mozilla.org/en-US/kb/https-only-prefs