Hey guys, today i bought a kindle KT3, it came with firmware 5.8.10. Haven't activated or connected it to wifi. I followed this wiki page
https://wiki.mobileread.com/wiki/5_x_Jailbreak and installed factory fw, it installed normally and after that i ran universal jailbreak and everything worked out fine. I'm now proudly jailbroken. Just wanted to report my success, thank you all