When do Mages learn Frostfire Bolt?

Rank 1 at level 40, with later ranks at 50, 60. Visit a class trainer in any capital.

Did Frostfire Bolt change from Classic?

Frostfire Bolt is new in WoW Forever and had no Classic 1.12 equivalent for Mages.

Rank	Level	Cost / range / cast	Effect	Classic 1.12
Rank 1	40	205 Mana · 35 yd range · 3 sec cast	Launches a bolt of frostfire at the enemy, causing 102 to 118 Frostfire damage, slowing movement speed by 40% and causing an additional 27 Frostfire damage over 9 sec. This spell will be checked against the lower of the target's Frost and Fire resists and counts as both Frost and Fire damage. Coefficient 81.4% of spell power (direct)	new
Rank 2	50	285 Mana · 35 yd range · 3 sec cast	Launches a bolt of frostfire at the enemy, causing 181 to 209 Frostfire damage, slowing movement speed by 40% and causing an additional 39 Frostfire damage over 9 sec. This spell will be checked against the lower of the target's Frost and Fire resists and counts as both Frost and Fire damage. Coefficient 81.4% of spell power (direct)	new
Rank 3	60	370 Mana · 35 yd range · 3 sec cast	Launches a bolt of frostfire at the enemy, causing 270 to 314 Frostfire damage, slowing movement speed by 40% and causing an additional 57 Frostfire damage over 9 sec. This spell will be checked against the lower of the target's Frost and Fire resists and counts as both Frost and Fire damage. Coefficient 81.4% of spell power (direct)	new

Missile Barrage (Arcane row 2): Gives your Arcane Blast spell a 40% chance, and your Arcane Wrath, Fireball, Frostbolt, and Frostfire Bolt spells a 20% chance to reduce the channeled duration of your next Arcane Missiles spell by 50%, reduce the Mana cost by 100%, and missiles fire every 0.5 sec.
Accelerant (Fire row 1): Reduces the casting time of your Fireball, Frostfire Bolt, and Arcane Wrath spells by 0.5 sec.
Heating Up (Fire row 4): Non-periodic critical strikes with Fireball, Frostfire Bolt, Fire Blast, and Scorch reduce the cast time of your next Pyroblast cast within 20 sec by 25%, stacking up to 3 times. Fire Blast grants an additional stack every time it deals damage.

Source: beta client 1.60.1.70753. Spell ID 1237313.