hear we need two different Domain.
lets assumed
Please change
http://XXX---yourDomain--XXX/child.html to http://domoin2.com/child.html
http://XXX---yourDomain--XXX to http://domoin2.com
First you run your http://domain1.com
and click "Start Communication" button
if you follow instruction correctly, you got success handshaking message.
then you start inter communication with both tab.