Your next Immolate, Incinerate, Conflagrate or Curse will hit all targets within 15 yards of the target and deal 43.40% of their normal damage.
Look to the sky... can you see it? Your salvation has arrived. — Tyrus Blackhorn (TCG)
Fire and Brimstone is a warlock ability learned at level 54 for those with the Destruction specialization. It grants [Immolate], [Incinerate], [Conflagrate], and curses the ability to hit all targets within range for roughly half the normal damage amount.
Patch changes
Patch 3.2.0 (04-Aug-2009): Reduced to 2/4/6/8/10% increased damage from Incinerate and Chaos Bolt on targets afflicted with Immolate, down from 3/6/9/12/15%.
Patch 3.1.2 (2009-05-19): No longer increases the damage of your Immolate spell, but now increases the bonus damage your Incinerate deals to targets afflicted by your Immolate by 6/12/18/24/30%.