When I log in remotely to my machine (via ssh) where galeon is already
running with windows open on the local X display (localhost:0) and then I
run galeon again it opens another window on the local X display rather than
the remote X display (localhost:10).

If I kill galeon and restart it, it respects the $DISPLAY variable and
displayes on the remote X display.

So the problem here is that the first instance was started with
$DISPLAY=localhost:0 and when I start the second instance from a remote
login ($DISPLAY=localhost:10) it contacts the existing instance of galeon
and gets it to open the new window. However, the old instance of galeon was
invoked with a different value of $DISPLAY so it gets displayed on the
wrong screen.

My guess at a fix would be that the protcol that galeon uses to contact
existing instances of itself should be extended to pass the value of the
$DISPLAY variable and then the new window should opened using that X display.

Steps to reproduce:
1 launch galeon
2 start up a new X server (eg XNest) for the same user
3 within the context of the different X server, launch galeon again
4 observe that the galeon window appear on the original X display
5 killall galeon
6 within the context of the different X server, launch galeon again
7 observe that this time the galeon window appears in the expected X display