WARNING: Attempting to flassh Magisk 16.3 Beta will brick your FireTV 1

[Sizzlechest]

I have attempted to flash Magisk in the past to see if it will work. It never did. The FireTV would just bootloop. I have always been able to boot back into recovery and flash the original boot image and then SuperSU to get back to normal. The latest Magisk 16.3 renders the FireTV unbootable. Luckily I had a USB A-A cable to fix it. AFAIK, Magisk can only work on Fire TVs with fully unlocked bootloaders, so I suggest only Fire TV 1 users attempt this.

In case you want to experiment:

Prepare:

1. Extract the bootloader_unlocked.img from the latest rom, assuming that's the one you have installed.
2. Send it to your FireTV using adb push boot_unlocked.img /sdcard/.
3. Put Magisk ZIP on the sdcard folder, too.
4. Put the latest working SuperSU ZIP on /sdcard too.

To install Magisk:

1. Reboot to recovery.
2. Install the boot_unlocked.img to the boot partition using TWRP.
3. Hit the escape key to back out and install the Magisk ZIP file.
4. Reboot the system.

To restore SuperSU, follow the directions for installing Magisk, but use the SuperSU zip file.

To recover from a brick:

1. Attach the FireTV to your computer with a USB A-A cable.
2. Go to the directory where the boot_unlocked.img file is located.
3. Run the following command: fastboot flash boot boot_unlocked.img
4. When it's done, reboot the FireTV.

 

[Sizzlechest]

Just tried Magisk 18.1 since it supports older versions of Android but it also bricks the device.