I really appreciate your response. I actually finally got the "Back" (or "Return") button to work by mapping the "Esc" button on the Flirc Full Keyboard to the "Return" button ("U" shaped arrow) on the Harmony One. I am using the "Guide" button on the Harmony as the "Home" button as well as the LCD screen "Home" button.
I recently "cut the cord" and needed the Harmony to seamlessly control TV and all Home Theater components. When watching broadcast or streaming programming, I am using the Fire Recast box for over the air local TV and FireTV for everything else. BTW, I had to update my old FireTV to a Fire Stick, in order to take advantage of some apps that were not supported on the 1st Gen FireTV. I didn't think it was possible to use a Flirc with a Fire Stick but I found this hack on YouTube https://www.youtube.com/watch?v=-vSwYeJd5fI&t=118s . It works!
Thanks again for taking time to respond.