Good guess--It stands for Fuller Emerson who must have made these caps.
The guy on e-bay only had it advertised as a Firebird cap in the body of the listing and not in the description so I believe most people missed this. I was just lucky to see it and recognize it.
![[Linked Image from img120.imageshack.us]](http://img120.imageshack.us/my.php?image=1968firebirdmc5.jpg)
![[Linked Image from img179.imageshack.us]](http://img179.imageshack.us/my.php?image=00000001kb0.jpg)
