Wrong, right and right, rather. Of course you're right about Ahura Mazda, I don't know what I was thinking of. However, Zoroastrianism is a monotheistic religion, a religion where only one God is worshipped. Fire is considered holy and a way to reach this God, but it's in no way worshipped. And yes, there are millions of them, especially in India and the States. Even some numbers in Iran (used to be many more though before 1979). The ones in India are called "Parsi", i.e. Persian by the locals, and are told to have their roots from ancient Persian refugees, from the Islamic conquest.
But the point is, fire-worshipper is completely incorrect, and was used as a derogatory term by Arabs for the Persians, just as the Persians used "Tazi" (Arab hound) for Arabs