Emma,
I was thinking, and perhaps F/A is Favourite/Added - in that they added it to their Favourites? I've never seen that acronym before.
To add: Call me silly, Emma, but I cannot keep up with all these Internet acronyms. Some people do not even try to converse anymore and simply speak in code.
LOL, ROFL, ROFLMAO, YMMV, SMH SMHL, YW, UR....and the list goes on and on.
Anyways, have fun!
* Michael, thank you for my oversight. :)