You can side-load our Android TV app to your Fire TV by downloading the APK from the address below. We will update the URL whenever the version number changes.

Here are the steps:

Find the Downloader app on Fire TV App Store and install it.

Now if this is a Fire TV that never had an application side-loaded, there are two things that needs doing first:

Go to: Settings → My Fire TV → About. Once there, click on the first item repeatedly. After about 7 times you'll see the message "No need, you are already a developer.

Settings → My Fire TV → Developer Options → Turn on "Apps from Unkown Sources"

Now select the newly appeared "Install unknown apps" menu item. Select the Downloader app and turn it on to allow the Downloader app to install apps.
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(Here's a guide with pictures from AFTVnews)

Then open the dialog box for entering a new URL

Enter the correct URL from above 👆. (Don't assume the URL in the picture is correct) Also you don't have to include https:// in the addres.

The hard part is over. You're almost done. Downloader downloads the APK file

Seeing it's an APK, It will ask you wether you want to install it or not

Click "INSTALL" and you are

Done.

P.S. If an app is side-loaded, meaning that it’s not uploaded from the Amazon store, it may come up with a low-resolution icon and unfortunately, we cannot do anything about this. :/