I'm also new to FLIRC and i'm trying to use it for this same purpose. I read the wonderful post describing how map the keys in the help section. I manged to get things coded up but when i went to test it i found that it's pretty much unusable. Most key presses behave very strangely. Either there are delays in how fast the fire responds, or the key is repeated.
I didnt have a lot of remotes lying around so i ended yup swiping codes for a Windows Media Center. From the info over in help thread it sounds like he experienced a similar issue and use an Apple TV remote for his directional keys.
What i think that i'm going to try to do is just choose a remote that i dont have and program that into the harmony and then use the harmony remote to emulate some other remote to program Flirc.
Has anyone tried that? And does anyone have a suggestion of a remote to emulate that actually works with the Flirc/FireTV that doesn't duplicate key presses?