In this section we will briefly talk about FrostFire specialization (LB FFB) in the Wrath of The Lich King expansion, specifically in the 3.3.5a patch.
It's the third of the 3 competitive mages PVE spec, it exists for two main reasons. One is historic, it was developed on private servers when the available realms were not bug-free enough to properly run TTW Fire, as Torment of the Weak wasn't triggering on attack speed-slowed targets, only on motion slowed one, and bosses cannot be slowed. The second reason why it can still be occasionally useful, is the movement slow provided by Frostfire Bolt, which is useful on adds and do doesn't lead to a dps loss. But just remember that now the Fire spec simply ouperforms the Frostfire spec, with exactly the same strength and weakness. Moreover you will gain range and the focus magic buff by playing Fire.
On this page I will not talk about gameplay, only about the specific optimizations for FrostFire Spec. For the gameplay, look at the Fire Spec page and replace Fireball with FrostFire Bolt. Consider that if a point mentioned in the Fire Spec page is not mentioned here, it is just the same (or barely different).