Possible way to downgrade your kindle on 5.8.10

I have a kindle voyage which run on 5.8.10 now, I want to jailbreak it, but found the firmware update_KV_5.5.0_initial.bin always disappear when I disconnect the USB.

So next time I did not to disconnect USB, and long press the power button to let it reboot without disconnect, seems it can flash the firmware, however, it report me ERROR 16 after flash, and it let me reboot to my 5.8.10 without problem.