I like the DVR management through the Xfinity App better than launching http://xfinitytv.comcast.net/tv-listings in a web browser so I started looking at the xfinitytv.ipa and found the url handler.
Install the Comcast Xfinity TV Remote via itunes and configure
Create a new activity or place in an existing, you can even make it one of your startup commands
Edit/add new activity, select add command
choose url, click url and enter: xfinitytv://
in the opens box, select “in safari”
save your changes