KerbyServer

The best way I have found to enable NFS on a Fedora system that has a firewall is to manually assign some of the NFS ports that are usually auto-negotiated and open just those ports in the firewall.

To do this, you can use Fedora's gui tool: system-config-nfs. In that interface, you can adjust the Server Settings as in the following screenshot:

...or just edit /etc/sysconfig/nfs to read:
LOCKD_TCPPORT=4001
LOCKD_UDPPORT=4001
MOUNTD_PORT=4002
STATD_PORT=4000


Then configure iptables or another firewall to open TCP ports 111,2049,4000,4001, and 4002 as well as UDP ports 111,2049, and 4002. In my experience, this enables both Linux and Mac OS X clients to connect to the NFS server, whereas different settings are not as compatible.