Yes, I have the Player app alreadly loaded on my Kindle, but I have been unable to find an .apk file for the TV app anywhere. Everything just points back to the Google Play store, and since I don't have another Android device, that doesn't help me.
I'm comfortable with side-loading apps, but without the .apk file, I'm kinda stuck. I'm not keen on rooting the device while it is still under warranty.
Just search for Xfinity in the Kindle App store - no need to side load anything, it should just download and install.
The only issue on Kindle Fire is that live TV does not seem to be supported. I couldn't get live TV to work inside the browswer app "Silk". The Xfinity web page actually thought I was a linux user and didn't detect that I was on a Kindle. It pushed me to download Silverlight which you can't do on a Kindle. Hopefully they fix this and move live TV watching to the Xfinity App.