Blizzard attempted to fix the focus magic exploit, where you can be frostfire with focus magic on another person, and it was thought that they did for a while. However, there is still a small loophole in the system. This requires the other mage to use focus magic in their main spec.
The frostfire mage specs into his focus magic spec and casts it on the other mage who uses focus magic in their main spec. At this point, the frostfire mage specs back into frostfire, and the other mage casts focus magic on him. Due to some odd buff checks performed, both mages will still retain focus magic and the 6% crit with procs.
This is working as of 5/10/09