Forwarding Firefox over X11 _sometimes_ works. Sometimes Firefox on the remote machine will try to join the session of your local firefox -- but fail and then complain that there's Firefox already running. Adding `--new-instance` helps if Firefox is running in a container and X11 socket file is forwarded to the container but it doesn't seem to help if X11 is forwarded over SSH.
Firefox is running on the remote, connected to a different X11 session. It is not running on the local. When I use `firefox --new-session --no-remote` on the remote, I see a dialog pop up on my local machine stating Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system.
Yes, this is because firefox doesn't allow multiple ff instances to use the same profile at the same time. You can ask firefox to create a new profile (`firefox -ProfileManager`) and then use a seperate profile for the remote instance
