The Firehead's Island really had nothing special on it. No Rahi, not even inhabitants anymore. It was rather of a hill rising from the ocean than an island. The island really was a hill, with the Firehead's Fortress on the top. Besides the fortress there was only rock... plain rock on the island. The island wasn't very big, it was smaller than many other islands. But it was big enough to hold the fortress. It has later been confirmed that the Firehead's Island was actually just a part of the Matoran Universe that was above the sea.