Anyway, fire is really deadly in this game, I feel like. My brother has less trouble fighting Frost Dragons (most likely because he's a Nord, and they have an innate resistance to Frost), than fire breathing dragons, but I do too, and I'm an Imperial.
It's possible that 'Fire Wizard' was a Dragon Priest with his annoying fireball staff I just saw my brother fight. Unless you weren't in Shearpoint.
I'm playing as an nord as well, and I know my character have an better resistance to frost, the real problem is the dragon bite, it's way too powerfull, I get killed in two hits!