For 5.12.2.1.1, and anything between 5.10.3 and 5.13.3 (inclusive) should try this KindleBreak JB
https://www.mobileread.com/forums/sh....php?p=4105735. This JB method doesn't require software rollback at all.
BTW, firmware version 5.8.8 or later won't allow you to install an earlier software update.