OT: X-application over ssh tunnel

[Hiisi]

Dear list!
Sorry for off-topic. This list is a grate source of knowledge and I
hope you're not very irritated by this off-topic.
Network setup:
A -> B -> C
Host A can connect to host B but not to host C directly. So, I do the
following. First, from host C I connect to B:
ssh -R 10002;localhost:22 user at B
When I need to connect to C from A first I connect to B:
ssh user at B
And from there I can go to C:
ssh user at localhost -P 10002
This thing, as you can see, is a classical ssh tunnel. However I would
like to use X applications on C from A, i.e. starting graphical
applications like firefox or rdesktop. Using -X when connecting to
each machine doesn't help. Could anybody provide me some hint on it?
TIA
-- 
Hiisi.
Registered Linux User #487982. Be counted at: http://counter.li.org/
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Spandex is a privilege, not a right.