In DragonVale for the iPhone and iPad, the Frostfire Dragon is a hybrid dragon with the cold and fire attributes, similar to the Blue Fire Dragon.
To get a Frostfire Dragon, you need to breed a Cold Dragon with a Fire hybrid. Some examples are Cold + Firefly, Cold + Lava, Cold + Blazing, etc.
Note that any of these combinations do not guarantee results, and the different combinations have different percentages for success. Keep trying though and you’ll eventually get your Frostfire Dragon.
Check out my DragonVale Breeding Guide for more dragon breeding combinations.