i think i bricked my device, at least i am stuck at fastboot after step 4.
all was fine until i started task 4. since i had the "cannot open for read: No such file or directory" message i started the "extra work needed". after adb push of "aboot" and "twrp" i restarted the device.
i started then again with "dd if=/sdcard/twrp_cubed.img of=/dev/block/platform/msm_sdcc.1/by-name/recovery
"dd if=/sdcard/aboot_vuln.mbn of=/dev/block/platform/msm_sdcc.1/by-name/aboot
but both times the numbers of the records in and out did not match with the ones in the description of the task.
Since it got late i wanted to stop again and try at some other time. sadly now i am stuck at the fastboot screen when i try to reboot the kindle fire.
when i plugg it to the pc it get recognized and get the "ready" on screen but can not find it by "adb devices". anything i can do?