See the comparison between the killing of the Hebrews, at the time when Moses was sent floating down the Nile, and the killing of Egyptian firstborn sons. Notice the day of passover with the blood over the door posts and the day Christs blood was shed and applied to the believer's heart, and the blessed believer found in Christ on the day of judgement.
to understand the significance of killing a first born you must understand the cultural significance of the first born. The first born was given special rights, privileges, and responsibilities. He was given a double portion of the estate and was considered the ruler of his younger siblings.
when the first born of egypt were killed it was saying "I am crushing you and taking away your posterity" (very harsh!)
Jesus being the first born says (on just surface level)... that He was the only BEGOTTEN Son (we are adopted) and that He is the ruler of all. Along with many other levels of meaning I don't feel the need to go into. lol