[Fire HD 8 and HD 10 General] Banana Joe:
So I've been following a few guides and tutorials here trying to get my Kindle Fire closer to a stock Android experience, and am very pleased with the results. If you just received yours, DO NOT LET IT GO ONLINE at any costs before disabling auto-updates, because it's only possible to uninstall system apps on FireOS 5.4.0 and lower (luckily got mine with 5.3.3 in it). As the title states, ROOT ISN'T REQUIRED. I've done this on an HD8, but have been informed that it should also work with the HD10 (which is now rooted,).

I removed pretty much everything Amazon, except for the shopping app, camera and calculator. Everything else works as expected on a snappy Android tablet.

Proceed with the following steps in order:

1) As soon as you first turn your tablet on, SKIP REGISTRATION and don't connect it to your router;

2) Open "Settings", go to "Device Options", click "Serial Number" about 7 times until "Developer Options" become enabled, go into it and "Enable ADB";

3) Go back to "Settings", "Security" and enable "Apps from Unknown Sources";

4) Connect your tablet to your pc and open an ADB Shell;

5) Paste the following commands in your shell to start uninstalling:

pm uninstall --user 0 com.amazon.device.software.ota
pm uninstall --user 0 com.amazon.kindle.otter.oobe.forced.ota
pm uninstall --user 0 com.amazon.settings.systemupdates
pm uninstall --user 0 com.amazon.kindle.otter.oobe
pm uninstall --user 0 com.amazon.kor.demo

pm uninstall --user 0 amazon.alexa.tablet
pm uninstall --user 0 amazon.jackson19
pm uninstall --user 0 com.amazon.advertisingidsettings
pm uninstall --user 0 com.amazon.ags.app

pm uninstall --user 0 com.amazon.client.metrics
pm uninstall --user 0 com.amazon.client.metrics.api
pm uninstall --user 0 com.amazon.cloud9.systembrowserprovider
pm uninstall --user 0 com.amazon.csapp
pm uninstall --user 0 com.amazon.dee.app
pm uninstall --user 0 com.amazon.device.backup
pm uninstall --user 0 com.amazon.device.backup.sdk.internal.library
pm uninstall --user 0 com.amazon.device.crashmanager
pm uninstall --user 0 com.amazon.device.logmanager

pm uninstall --user 0 com.amazon.dp.fbcontacts
pm uninstall --user 0 com.amazon.dp.logger
pm uninstall --user 0 com.amazon.geo.client.maps
pm uninstall --user 0 com.amazon.geo.mapsv2
pm uninstall --user 0 com.amazon.geo.mapsv2.services
pm uninstall --user 0 com.amazon.kcp.tutorial
pm uninstall --user 0 com.amazon.kindle
pm uninstall --user 0 com.amazon.kindle.devicecontrols
pm uninstall --user 0 com.amazon.kindle.kso

pm uninstall --user 0 com.amazon.kindle.personal_video
pm uninstall --user 0 com.amazon.legalsettings
pm uninstall --user 0 com.amazon.logan
pm uninstall --user 0 com.amazon.mw
pm uninstall --user 0 com.amazon.mw.sdk
pm uninstall --user 0 com.amazon.ods.kindleconnect
pm uninstall --user 0 com.amazon.photos
pm uninstall --user 0 com.amazon.photos.importer
pm uninstall --user 0 com.amazon.precog
pm uninstall --user 0 com.amazon.readynowcore
pm uninstall --user 0 com.amazon.recess

pm uninstall --user 0 com.amazon.socialplatform
pm uninstall --user 0 com.amazon.unifiedshare.actionchooser
pm uninstall --user 0 com.amazon.unifiedsharefacebook
pm uninstall --user 0 com.amazon.unifiedsharegoodreads
pm uninstall --user 0 com.amazon.unifiedsharesinaweibo
pm uninstall --user 0 com.amazon.unifiedsharetwitter
pm uninstall --user 0 com.amazon.vans.alexatabletshopping.app
pm uninstall --user 0 com.amazon.venezia
pm uninstall --user 0 com.amazon.webapp
pm uninstall --user 0 com.amazon.webview
pm uninstall --user 0 com.amazon.webview.metrics.service
pm uninstall --user 0 com.amazon.whisperlink.activityview.android
pm uninstall --user 0 com.amazon.whisperlink.core.android
pm uninstall --user 0 com.amazon.whisperplay.contracts
pm uninstall --user 0 com.amazon.zico

pm uninstall --user 0 com.audible.application.kindle
pm uninstall --user 0 com.goodreads.kindle
pm uninstall --user 0 com.kingsoft.office.amz
pm uninstall --user 0 jp.co.omronsoft.iwnnime.languagepack.zhcn_az
pm uninstall --user 0 jp.co.omronsoft.iwnnime.mlaz
pm uninstall --user 0 org.mopria.printplugin

pm uninstall --user 0 com.amazon.accessorynotifier
pm uninstall --user 0 com.amazon.device.messaging
pm uninstall --user 0 com.amazon.device.messaging.sdk.internal.library
pm uninstall --user 0 com.amazon.device.messaging.sdk.library
pm uninstall --user 0 com.amazon.device.sync
pm uninstall --user 0 com.amazon.sync.service
pm uninstall --user 0 com.amazon.securitysyncclient
pm uninstall --user 0 com.amazon.sync.provider.ipc
pm uninstall --user 0 com.amazon.device.sync.sdk.internal

pm uninstall --user 0 com.amazon.communication.discovery
pm uninstall --user 0 com.amazon.tcomm
pm uninstall --user 0 com.amazon.kindle.rdmdeviceadmin
pm uninstall --user 0 com.amazon.kindle.cms
pm uninstall --user 0 com.amazon.providers.contentsupport
pm uninstall --user 0 com.amazon.android.marketplace

pm uninstall --user 0 com.amazon.device.settings
pm uninstall --user 0 com.amazon.device.settings.sdk.internal.library
pm uninstall --user 0 amazon.speech.sim
pm uninstall --user 0 com.amazon.knight.speechui

pm uninstall --user 0 com.amazon.h2settingsfortablet
pm uninstall --user 0 com.amazon.avod
pm uninstall --user 0 com.amazon.kindle.otter.settings
pm uninstall --user 0 com.amazon.mp3
pm uninstall --user 0 com.amazon.parentalcontrols
pm uninstall --user 0 com.amazon.pm
pm uninstall --user 0 com.amazon.tahoe
pm uninstall --user 0 com.amazon.weather
pm uninstall --user 0 com.android.backupconfirm
pm uninstall --user 0 com.android.sharedstoragebackup
pm uninstall --user 0 com.android.calendar
pm uninstall --user 0 com.android.contacts
pm uninstall --user 0 com.android.deskclock
pm uninstall --user 0 com.android.documentsui
pm uninstall --user 0 com.android.email
pm uninstall --user 0 com.android.onetimeinitializer
pm uninstall --user 0 com.android.wallpapercropper
pm uninstall --user 0 com.android.providers.downloads.ui
pm uninstall --user 0 com.android.music

You should see a message stating "Success" after every package is successfully uninstalled for "user 0" (they're still in there if you do a factory reset, so in this case you have to repeat the whole process to avoid updating, but they're removed for the current user).

6) At this point it should be safe to go online. Reboot to recovery, wipe cache and restart, and then connect to your router. Your home button won't work at this point, but the process is straight forward enough so you won't need it for a while;

7) Open your "Silk Browser" that shouldn't have been uninstalled yet. Use the guide in this page and get "Play Store" up and running;

8) Open "Play Store", install "No-Root Firewall" to control who or what goes online, install Firefox (or your preferred browser) and continue setting up through it just to avoid exposing our process too much, since Amazon tracks Silk navigation in their "optimization" processes!

9) Open Firefox from the notifications bar (remember, your home button still doesn't work so don't mess up clicking around), and download and install apks for "Trebuchet" from here and "Launcher Hijack" from here. I prefer using this ported version of Trebuchet instead of "Nova" or "Evie", firstly because it's the one from Lineage 15.1, pretty, light and fast, and secondly because it isn't tracking anything or sending any collected info to any server, just as a launcher should. Open "Launcher Hijack" from the notification bar, configure "Trebuchet" to be your launcher, and your home button will regain functionality;

10) Reboot to recovery, wipe cache and restart, and we'll have another round of uninstalling:

pm uninstall --user 0 com.amazon.cloud9
pm uninstall --user 0 com.amazon.cloud9.kids

pm uninstall --user 0 com.amazon.firelauncher

Notice we've done away with "Silk Browser" and the infamous "Fire Launcher". Reboot to recovery, wipe cache and restart once more to see you only have one launcher;

11) Last round of uninstalling (for some reason, some of these wouldn't go away in the earlier rounds):

pm uninstall --user 0 com.amazon.kindle.unifiedSearch
pm uninstall --user 0 com.amazon.alta.h2clientservice
pm uninstall --user 0 com.here.odnp.service
pm uninstall —-user 0 com.amazon.kindleautomatictimezone
pm uninstall -—user 0 com.amazon.bluetoothinternals

12) I've kept a tiny bit of Amazon software behind, you can do away with it if you please (just make sure to install "GBoard" or another keyboard from the Play Store before removing the standard one):

# Fire Standard Keyboard
pm uninstall --user 0 com.amazon.redstone
# Amazon System WebView
pm uninstall --user 0 com.amazon.webview.chromium
# Shop Amazon
pm uninstall --user 0 com.amazon.windowshop
# Calendar Storage
pm uninstall --user 0 com.android.providers.calendar
# Contacts Storage
pm uninstall --user 0 com.android.providers.contacts
# Calculator
pm uninstall --user 0 com.amazon.calculator
# Camera
pm uninstall --user 0 com.amazon.camera
# Contact Sync Adapter
pm uninstall --user 0 com.amazon.dp.contacts

That's it! The end result should be very close to stock feeling, debloated. I keep "No-Root Firewall" just to make sure I choose what goes online and when. At the moment of writing, there's just one single remaining service full of permissions called "amazon.fireos" that tries to phone home infrequently, but that one you can't uninstall without going into a bootloop...

Most of the info was compiled and tested with support from the following thread, so thanks go to everyone who contributed. Special thanks go to DragonFire1024 for all the work he's put into Fire devices ;)