First of all use a soft brush set at about size 150, and make a white blob in the middle of a black canvas.

Now add a color balance with these settings:

Shadows: +94, +4  , -100

Midtones: +77,0,-71

Highlights: +20, +2, -45

(preserve luminosity unchecked).

Now gaussian blur it with 6.0 Pixels.

Now smudge the center to the bottom left slightly, and then smudge the back to the top right, to create a motion effect.

Now to give it a really nice effect add a black and white gradient map set to overlay and sharpen the fireball layer.

Hope you enjoyed!