New owner, hello.  I am having a heck of a time getting my new flirc to work with my Harmony 300 remote and the 4th gen fire tv 4k.  The Firetv is in the back of the tv powered with an OTG cable and a short USB extension so the flirc faces out of the front of the TV within 10 feet and line of site.  The device was added to the harmony as flirc and model firetv (I tried xmbc as well).  It's not responding at all, but the firetv is fine as it responds to the OEM remote.  I do have ADB debugging turned off in the device settings, it's been rebooted, all to no avail.  I gotta be missing a step somewhere.... any advice or help appreciated.  

bump... help... thx

Change or (preferably) remove the USB extension cable. Don't worry about the line of sight. Flirc's IR receiver is really sensitive and will work even when Flirc is behind the TV.