Time to contribute once again. The topic speeks for itself, I've got this told by a guild mate who is currently using this on our Lich King 25 HC progress. So creds to him. Some might see this as common sense, but it isn't since the bonus crit should disappear after you switch gear.
What to do:
1. Equip 2p Tier 9 (Mage only)
2. Buff Molten Armor
3. Switch back to normal gear
4. ???
5. Gain 1-2% crit depending on your spirit.