HI John Bunch: Please file a bug in bugzilla for this: https://bugzilla.mozilla.org/enter_bug.cgi Cheers! ..Roland

I assume the HRIS server is on the LAN. Firefox doesn't determine the IP address through which it accesses a web server. Your scenario suggests that the request is routing out through the firewall onto the public internet instead of staying within the LAN. DNS-over-HTTPS (DoH) requests the HRIS server address from Cloudflare (or another provider) on the public internet. If the query fails, then Firefox should fall back to the local system for DNS. It sounds as though the customer may have public DNS configured for the hostname used by HRIS, in which case Firefox will obtain that public address and never learn the internal address. If it is necessary to have an external DNS entry for this internal server, and the router cannot intercept the outbound Firefox request and keep it inside the LAN, I think your customers will need to manage their users' Firefox installations either by blocking DoH or by setting a hostname exception. ''See:'' https://support.mozilla.org/en-US/kb/dns-over-https-doh-faqs#w_how-does-firefox-handle-split-horizon-dns ''To block DoH:'' * https://github.com/mozilla/policy-templates#dnsoverhttps * [[Customizing Firefox Using Group Policy (Windows)]] ''To exclude specific hostnames:'' * https://support.mozilla.org/en-US/kb/firefox-dns-over-https#w_excluding-specific-domains * [[Customizing Firefox Using AutoConfig]]