They had been fighting over Vito Giac's rackets (and legitimate endeavors) since Vito's death in early '12. Eventually, from what I understand, it all went too far and Jackie shelved Frankie. Frankie became the captain of Vito's crew when he went to prison after the Gamtax case, and they were VERY close friends. Historically speaking, it does seem like Jackie's a greedy guy, so none of this should be a surprise.

As for their operations, like I said before: mostly bookmaking, shylocking, and extortion. Of course, individual members are into some other crimes, but it's mostly the standard rackets.