flyingflirc - Just wanted to say I was able to use your suggestion and it worked perfect. While I didn't have an older IR Roku remote to use (mine are all motion so they use Wi-Fi direct) I did have my Harmony set with a Roku config for all buttons. I had just swapped my Roku 3 for the fireTV (I was using the fireTV remote while I worked on getting my FLIRC properly configured) so I just used the Harmony to send the codes to my FLIRC and then tested. ABSOLUTELY flawless ! Now I will simply rename the device/activity to fireTV.
Since this worked it actually makes adding the fireTV to a Harmony super easy, even if you don't have access to an older IR Roku remote:
1) Add a Roku to your Harmony (I used the Roku 3).
2) Rename the device to fireTV
3) Add activity, map the Roku keys to whatever keys/soft buttons you want [NOTE the fireTV button that looks like 3 horizontal lines should be mapped to the Roku * (asterisk) button]
4) Use Harmony to program your FLIRC
5) Put into fireTV USB port and test
Thanks again for the great help !!