That button grays out when both profiles are running. Try it.
Also if the firefox instance is launched with no-remote, this won't even work as expected. Instead it'll start another firefox instance with remoting enabled, which will fail to start because the profile is already in use.
Also if the firefox instance is launched with no-remote, this won't even work as expected. Instead it'll start another firefox instance with remoting enabled, which will fail to start because the profile is already in use.