When users are using RED in DHCP/PPP mode, the received DNS servers need to be written to /var/ipfire/dns/servers and being marked as coming from there. When the DHCP lease expires or the PPP session ends, they will need to be removed again and unbound needs to be reloaded.
The ISP assigned DNS Servers now will be "/var/run/dns1" and "/var/run/dns2". The addresses will be picked from there and used by the CGI and script files. https://git.ipfire.org/?p=people/stevee/ipfire-2.x.git;a=commit;h=1434fa0df5ab01c2e3a430f05db159a3a82bc3ba
https://blog.ipfire.org/post/ipfire-2-25-core-update-141-release