[Fire HD 8 and HD 10 General] pastorbennett:
UPDATE: Unfortunately, this won't disable OTA and the Lockscreen ads. I had an amazing stroke of luck that somehow, the uninstall command for OTA and the ads was successful on 2 of the 3 tablets I bought. With the third, it didn't take long for the ads to come back after disabling, so I spent the $15 to remove the ads. This script will still work to install Google Play Store and Launcher Hijack. Thanks to [MENTION=4859884]Gilly10[/MENTION] and [MENTION=8089882]BaronKiko[/MENTION] for their work.

I put together this tool for my own personal use, and thought it would be helpful to many, so I'm sharing it here. I tested it both on macOS 10.13 and Windows 10 x64. I have not tested on Linux, though it should work. The only additional step you may need for Linux is to have a Linux specific ADB executable, though I would think the macOS ADB is the same.

First, I take no credit for any of this, aside from writing the script and putting together this guide, as everything here was compiled from information I found on other threads. I hope you find this useful.

Just a quick note, I ordered a 3 pack of the 2017 HD 8 tablets, and on two of them, I was able to fully uninstall Amazon OTA and Lockscreen without root access. On the third, though, I could only disable them. The end result should be the same. Also, it might be necessary to complete the initial setup of the tablet, including connecting to the internet, for this to fully work. Though this will update to FireOS 5.6.0.0, the script should work just fine, as I did the initial update on all 3 of my tablets. There is one caveat to this, however: the script may not work to disable OTA for future updates beyond 5.6.0.0. Additionally, some are reporting that the OTA is still enabled, even after the script executes. This may very well be possible, though I'm not able to test it at the moment. As a precaution, it's recommended that you install NoRoot Firewall and block the following apps:

com.amazon.device.software.ota
com.amazon.kindle.otter.oobe.forced.ota
com.amazon.kindle.kso

When running this tool, the script will install the needed files for the Google Play Store, as well as Launcher Hijack. Then the script will disable the Amazon OTA and Lockscreen packages, followed by an attempt to uninstall OTA and Lockscreen. Also, I apologize for the image sizes, for some reason they're appearing larger than the actual size.

CLICK TO DOWNLOAD TOOL
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First, you'll need to prepare your Fire tablet before doing anything else.

Step 0: If you're running Windows, you'll need to first in stall the ADB driver (Fire_Devices ADB drivers.exe) included in the zip file. For Mac and Linux, ADB should work without any other requirements.

Step 1: Enable Developer Options. To do this, in Settings, navigate to the Device Options menu, scroll down and tap Serial Number 7 times.

Step 2: Enable ADB. After enabling Developer Options on the Device Options menu, navigate to the Developer Options menu and tick the "Enable ADB" option.

Step 3: Enable Apps from Unknown Sources. In Settings, navigate to the Security menu and tick the "Apps from Unknown Sources" option.

Step 4: Run the install script. For Windows, simply double-click on "install.bat." For both macOS and Linux variants, in the terminal, navigate to the folder where you unziped the tool, and run the following command:

sh install.sh

After the script completes successfully (you will probably get an error when the script attempts to uninstall the Amazon OTA and Lockscreen apps), you may chose to reboot your Kindle Fire at this point, though it isn't absolutely necessary.

Step 5: Run Google Play Store. At first, it may take a little patience. If you get a blank white screen, exit the app and try again. Once Google Play Store is set up with your Google account, you're ready for the next step.

Step 6: Install Launcher. Before you're able to have the option to enable the Home Button, you'll need to install a launcher from the Play Store. I prefer Nova Launcher, but of course, you're free to use whatever launcher you prefer. After installing a launcher, you'll need to open the launcher. IF YOU DON'T OPEN THE LAUNCHER AFTER INSTALLING, THE OPTION TO DETECT THE HOME BUTTON WILL BE UNAVAILABLE.

Step 7: Enable Detect Home Button Press. Open Settings and navigate to the Accessibility menu. Scroll down to Services, and tap the option "To detect home button press."

Step 8: Set Home Launcher. This step may be unnecessary, depending on what launcher you choose. If Launcher Hijack doesn't redirect home button presses to the new launcher you installed, you may need to open the Launcher Hijack app and select your launcher.

If you've done everything correctly, your Kindle Fire HD should feel almost just like any other Android tablet.