It is pretty easy to do once you understand the convoluted process. Some Tips (or more confusion):
Tonyski has it figured out. Use his chart.
Flirc needs a "forced update" of its firmware in its options. No do, no work.
The confusing part is the Remotes. My goal was to get my Harmony One to run a FireTV Activity, i.e., turn everything on and switch everything to the correct settings. For me that is TV on, HDMI 1; Soundbar on, Optical on; Video switcher On, Output 3; FireTV Home, Audio Optical.
The Harmony One has an canned profile for Flirc, XBMC. I started with that.
Next, I needed ANY old IR remote laying around to learn the Flirc commands in Tonyski's great chart. I used an old MSMC remote and used the Flirc GUI to teach its keys the Flirc commands from the chart. I used matching buttons where possible for intuitiveness but it makes no difference. Use all numbers if you want.
For some reason you cannot program the Menu key with the GUI. You must use the old DOS commands. In current versions of Windows you do that by running CMD.exe. You can type cmd in the search window or do a Win + R and enter cmd.exe. Enter the commands from the C:\ prompt Tonyski has listed. Push a key on the "old" remote you want to be Menu.
Next, I went into my Harmony One GUI and had it "learn" the commands from the "old" remote to its FlircXBMC device profile. I then setup an Activity to do everything when I selected FireTV.
If I helped, great. If not, sorry. It ain't easy. Flirc should write a canned profile for us.
Maybe of interest, my old MS Entertainment Keyboard and Mouse 7000 will also talk to FireTV. I think it will also take files from a USB drive. I've ordered a cheap hub from Amazon to see if I connect Flirc(Harmony One remote), the MS KB/Mouse and a USB drive with files, music and photos and see what happens. It is supposed to work. Moral, don't throw away old electronics. It can live again.