Xumo TV a great application with lots of free content.
Features
Works on 4K Firestick, 2nd Gen Cube, Nvidia Shield, Chromecast Google TV
(APK at the bottom of the page)
Steps to confirm your Device IP address and confirm ADB is enabled:
1. From the Main Menu scroll to hover over Settings.
2. Click My Fire TV.
3. Choose Developer Options.
4. Click Apps from Unknown Sources.
5. Choose Turn On.
6. Go to About — Network and confirm your IP Addresss
Install the APK from the link below