It stood for Mortal Kombat: Federation of Martial Arts, which, if I'm not mistaken, was a feature on the official MK web site where users would "vote" on battles between two given characters... And later a video would be released presenting the fight.

People would not vote on fights however, they'd simply purchase the kombatant's stocks (obviously with fake currency, if I'm not mistaken it was called Atman, named after an MKC producer called Steve Hattman). After you purchased fighter stocks with atman, your cash would increase if your fighters won the matches.

FoMA is where Jax went on trial for performing a fatality.

That was pretty stupid... it wasn't a fatality though if I recall correctly. Sub-Zero was about to kill Sonya in a tournament match and Jax interfered, saving Sonya, yet breaking the sacred rules of Mortal Kombat. Therefore, he was sentenced to trial, but it was discovered that it was Tremor disguised as Jax all along, meaning Jax was innocent.

I didn't see very many episodes.
I just remember Jax marching around talking smack and saying, "Where's Rain?" over and over, and then the trial.

I thought he was on trial for killing him (outside of battle).

Pretty cool for a web feature, though.
It'd be great if they'd slap these on a DVD as extras, or something.

No, that was his tournament battle with Rain. Another joke.
Matches were always split into three parts, round one, round two, and round three (with the exception, I think, of only one match, and that is Rain vs. Quan Chi). The first round of Jax vs. Rain was just Jax going ''Hey where's Rain? About time Rain showed up, where's Rain? HEY RAIN! WHERE'S RAIN!'' and then Rain shows up from the skies, and attacks Jax from behind. Then it's on to round two.

Jax didn't kill Rain, either. Rain was ''killed'' by Quan Chi in their match, got pwn3d really. Quan Chi just stood around and had green skeletons beat the crap out of Rain until he blew up from Quan Chi's magic. Later on, though, it was revealed that it was just a swerve as Rain was actually allied with Quan Chi during the chaotic times of Outworld with Shao Kahn away.