APKs on Android TV / Fire TV
Sideloading on a TV device works differently from a phone -- no touchscreen file manager by default, so this covers the two common methods: a file-manager app, or pushing the APK over the network with ADB.
1Enable apps from unknown sources
Settings > My Fire TV / Device Preferences > Developer Options > Apps from Unknown SourcesOn stock Android TV, Developer Options must first be unlocked by tapping the Build number 7 times under About, same as on a phone.
2Option A: install a file-manager app with a browser
Install a file manager from the Play Store that includes its own downloader (e.g. "Downloader" by AFTVnews, very common on Fire TV), then use it to browse to the APK's direct download link and install from there.
3Option B: push the APK over the network with ADB
Enable ADB debugging under Developer Options first, then find the device's IP address under Settings > Network.
adb connect <device-ip>:5555adb install path/to/app.apkYour computer and the TV device must be on the same local network for adb connect to work.
4Find the newly-installed app
Sideloaded apps often don't appear on the main home screen automatically -- check Settings > Applications > Manage Installed Applications, or install a launcher app that surfaces all installed apps.