Which Firstborns?

In Shmos 11:5 and 12:29, Rashi discusses why makas bechoros extended to all firstborns, even of the maidservants and the captives. This episode discusses the justice of this and deals with the question why the makkah would have extended to Jewish firstborns but for Hashem’s salvation (as indicted in Rashi on Bamidbar 8:17).