Lets say you have a set up at home and use a firewall (home1) and within the network you have a machine running X server (home2) and wish to run X server apps remotely from your work.
While many people can get X forwarding to work if Home1 had the xserver running, but what if home1 is a firewall and its home2 that has the x server?
Possible? YES
read on
Make sure you have X11Forwarding off on in your sshd_config
then
SSH from work to home1 and forward a port to home2's SSH server:
work$ ssh -L 2022:home2:22 user( at )home1
wham!