As I just have the Amazon FireTV as my Only Media Player in my House I got the need of controlling this device from openHAB. As it turns out, this isn’t as difficult as it seems.
You just need to enable the adb debugging feature on the FireTV and use shell scripts to send key codes.
Here is one example script, which simulates a press of the Play/Pause button:
adb tcpip 5555 adb connect firetv-office:5555 adb shell input keyevent 85 adb disconnect
In an openHAB rule you now just need to execute this script:
You can get an overview of the possible key codes on this site:
Maybe there is a better solution (maybe a virtual Player item and parameterising the shell script), but for now it works.