I have been able to get my Xfinity TV Go app working on the FTV.
1. Download the Xfinity.apk [Mediafire]
2. Buy or Download the "Mouse Toggle for Fire TV" [Google Play - $2.99]
3. Install Mouse Toggle on an android device (tablet or phone) and make sure you are on the same network as the FTV stick.
4. Follow instructions on the Mouse Toggle app (EXTREMELY SIMPLE)
5. Install the Xfinity.apk to the FTV via ADB
6. Open the Xfinity app on the FTV
7. If the Mouse Toggle installed and is running QUICKLY double tap <PLAY/PAUSE> and you will see a cursor on the screen. Move it with the D-Pad and select Username/Email
8. Login with your Comcast Account
I have done this and it 100% works! It is still a bit of a pain to have to switch to D-Pad mode to scroll and the Mouse Mode to select but all in all it works!
Thanks and any comments/feedback is greatly appreciated!