Kiosk firmwares can be only downloaded over a 3.55 OFW or under.
Anything above cannot be on a CFW. Most videos on Youtube that are showing you "confirmed JB 4.x" are mostly demonstration mode firmwares which are basically useless as you can only install signed .pkgs and cannot run homebrews.
So, without an E3 flasher and the knowledge on downgrading OR a PS3 with 3.55 OFW; you are hopeless on a jailbreak.