When active, all spells can be cast at a cost of zero MP.
When active, the casting of spells cannot be interrupted by melee attacks. Stun, sleep, and movement can still interrupt the spells though.
Often used as emergency casting of healing magic when all mages are spent on MP.
Sometimes used as a means of ensuring the success of a Warp or Escape spell.
/ja "Manafont" <me>
Since Manafont is a two hour special, some people prefer not to make a macro for it to prevent unintentional activation.
Some people prefer to put two hour job abilities on a trigger macro. This means they use the macro syntax /ja "Manafont" <stpc>, which makes the macro user have to select a player character to use the job ability on, increasing the safety of the macro.