[Lejo]

No, it is not a Fuel-Air bomb. I don't know where this idea comes from, but I've heard many people say it.

FAB is the Soviet designation for a general purpose high-explosive bomb. Any amount of research will confirm this.

For example:

http://vvs.hobbyvista.com/Research/Ordn ... /index.php

True, FAB means Fugasnaya Aviatsionnaya Bomba (=Aviation Demolition Bomb)
Maybe there is some confusion with the VAP-250 which is a napalm bomb and produces a fireball.