Hollytail and I have discussed this, but we haven't really come to a real conclusion. I don't think that Firestar's Warrior Name, Fireheart, is meant to describe him, as Firepelt or Firetail would've worked just fine. We both believe that Bluestar named him after another cat, either Oakheart or Lionheart.
Oakheart would work, considering he WAS Bluestar's mate, and his dream was always to be deputy (which, obviously, Fireheart later achieved). He was also described as "a great warrior", "fierce", "loyal", and "ambitious" (well, obviously not TOO loyal if he took Bluestar as a mate, but no hard feelings, Oakheart XD), which Fireheart was most of.
Lionheart would also work, considering he was a "great warrior", "fierce", "loyal", and he was Bluestar's deputy when he died. He was also one of the cats who first met Rusty in the woods (along with Graypaw and Bluestar), so Bluestar may have decided that Lionheart would be a good warrior for Fireheart to model himself after.
So, which one do you think?