Originally Posted by jschiwal
I have launched firefox in a remote ssh session and haven't noticed the problem, but I can't say whether firefox was already running on the remote machine before logging in.
If I understood well, you have to start firefox locally. Then ssh -X to a machine, start another firefox.
Via X message sorcery, firefox detects that it's already running and will open in the same instance rather than opening a new one.
Seems a bit strange but I've seen other people having the same problem. I can't check myself.