Here is my firehol.conf that allows multicast mDNS packets through:
# define mdns so we will accept it
server_mdns_ports="udp/5353"
client_mdns_ports="5353"
interface eth+ multi
policy return
server mdns accept
server multicast accept
interface eth+ home src "${home_ips}"
server all accept
client all accept
Initially I had the server mdns accept and server multicast accept inside the home interface, but this didn't work. Firehol's developer, Mr Costa Tsaousis, pointed out that src "${home_ips}" on home would exclude broadcast packets sent from MAC addresses, thus the second interface definition (multi).
Cheers,
Steve