Does "sysctl -w net.link.ether.bridge_ipfw=1" not work (anymore)?

Hi,

According to the ipfw man page I should be able to use:

sysctl -w net.link.ether.bridge_ipfw=1

in order to route the bridged packets to ipfw.

When I try that on (Mountain) Lion though I get:

net: class is not implemented

I am missing something?

Regards,

Dutch