I am running into the same problem. After installing openfire.tar.gz on c9.io, I don't get any response from the server when I do myproject.c9.io:9090.
netstat -an | grep 9090 shows
tcp6 0 0 :::9090 :::* LISTEN
Adding the line to the openfire comand file has no effect
DAEMON_OPTS="-Djava.net.preferIPv4Stack=true"