Back in the day (read: before the latest firefox update), I used to be able to ssh to a remote box, run 'firefox -local', and have that box fire up its own firefox session even if I was running firefox on the system from I which I sshed. Those days seem to be gone. No matter what I try, if I've got firefox running on my local desktop, the remote firefox command just fires off another instance of the local firefox session.
This is relied to the problem I have using "firefox -P" on my local centos to try to start a new instance of firefox with a different profile.
My solution is to start env MOZ_NO_REMOTE=1 firefox -P
Could you try that? I checked it through ssh and it works. Just that you have to chose the profile at start.
Anne