1. Download the app
Head over to github.com/sphinx02/FireStarter/releases and download the apk on your computer.
2. Sideload the apk
I like to use adbFire to do my sideloading, I made a tutorial here if you need it.
3. Launch Firestarter for the first time
On the Fire TV home screen, go down to 'Settings' and then over to 'Applications' and then down to 'Manage Installed Applications'. Find Firestarter and launch it.
Boom! A clean launcher focused on apps.
4. Configure the settings
By default, Firestarter will be configured to launch at boot or when the home button is pressed but you can change it to any app you want! You can also hide apps that you might just want to run in the background and many other options. Plus it has an integrated updater so you don't have to worry about sideloading it again whenever there is an update.