During the Age of Myth, Gorkamorka fought, catch and took a sun down from the sky. After succeeding he tried to eat a piece of its surface and discovered a new ability to spew waves of fire. The rites and rituals of the Firebellies originated from Ogors trying to replicate this legend of the Sun-Eater by breathing fire on their foes and going into combat.
Firebellies show their devotion to the Sun-Eater by praying to ash, flames, volcanoes and magma. They eat flammable fuel in magic rituals so that they can set their foes on fire and honor their god. Above all they seek to replicate the actions of their god and devour the sun, which the Mortal Realms has plenty in its countless skies. They hunt down sun located not so high and their priests may be able to catch them and bring them down.
In trying to replicate the actions of their gods the cults search for fireblood beasts, like Magmadroths, to devour. They also eat flammable minerals, spewing it forth in a wave of fire to spice these creatures and make them more tasty. When a meal is not completely edible, they soften the harder parts with huge basalt hammers.