Problem seeing network scanner thru firewall

[Sherman Grunewagen]

On an F18 machine I have an Epson WF3540 printer/scanner sitting on my LAN. Printing works.
I downloaded the free version of VueScan to try it out before purchasing, but it can't
see the scanner through the firewall.  It just reports "No scanner was found".

If I disable the firewall with  `systemctl stop firewalld.service'
then VueScan can see and control the scanner. I wrote the author of VueScan and he said:

    You need to configure the firewall so it lets VueScan communicate with the scanner through
    the firewall.  It's using mDNS UDP packets.

In the output of `iptables -L',  I see several lines that look like

       ACCEPT     udp  --  anywhere             224.0.0.251             udp dpt:mdns ctstate NEW

but I'm a firewall newbie and don't know what to do next.  Would someone
that understands please set me on the path to enlightenment. :-)  Thanks!

Sherman