You must export the tftproot, and any release installation directories. The following /etc/exports file corresponds to the provided farbot.conf:

/export/freebsd/netinstall/tftproot /export/freebsd/netinstall/6.1 /export/freebsd/netinstall/6-stable -ro -maproot=root -network 1
0.0.50.0 -mask 255.255.255.0

A simple dhcpd.conf that directs clients to the generated tftproot:

# dhcpd.conf
#
# Sample configuration file for ISC dhcpd
#

# option definitions common to all supported networks...
default-lease-time 600;
max-lease-time 7200;

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
authoritative;

# ad-hoc DNS update scheme - set to "none" to disable dynamic DNS updates.
ddns-update-style none;

option subnet-mask 255.255.255.0;
option routers 10.0.50.1;
filename "/boot/pxeboot";

subnet 10.0.50.0 netmask 255.255.255.0 {
  range 10.0.50.10 10.0.50.60;
  next-server 10.0.50.1;
  option root-path "/export/freebsd/netinstall/tftproot";
}

The following must be added to /etc/inetd.conf to support tftp access to the netbooting client:

tftp    dgram   udp     wait    root    /usr/libexec/tftpd      tftpd -l -s /export/freebsd/netinstall/tftproot