Frostfire bolt is taking the affect of piercing ice, but not Fire Power talent.
Frostfire Bolt tooltip at lv 50:
With Piercing Ice: 513 to 598 damage range
With Fire Power: 484 to 564 damage range.
484 * 1.06 = 513 and 484 * 1.06 = 598. So clearly, with fire power it is the base damage range.
I thought, maybe Fire Power does not affect tooltip and Piercing Ice does. I checked the tooltip changes for both fireball and frostbolt switching between piercing ice and fire power and both stay the same.
This would lead me to believe new runes display the increase modifiers in the tooltip and fire power does not affect frostfire bolt.