Benefit: When you have combat advantage against the target of your firepulse racial power, that power ignores any fire resistance or immunity possessed by the target.[MP:140]
This is rated as a terrible choice as the author strongly disagrees about playing a Genasi Rogue. [Char-op Genasi] A better rationale to rate this as terrible is to note that it is highly situational where only a small portion of monsters resist fire.