The current 1.1.3 version of my Downloader app in the Amazon appstore is not compatible with the new Amazon Fire TV 3. When you try to install an APK file within Downloader, the APK does not install and a message saying “No app found to handle this file” appears. I have fixed the issue and have already submitted an updated 1.1.4 version of Downloader to the appstore. The update just needs to be approved by Amazon first, which usually takes about 24 hours, so the update should be live tomorrow. In the meantime, you can use Downloader to download files as usual and then switch to the free app Total Commander in order to install APKs. Simply navigate to the “Internal shared storage” > “Downloader” directory inside Total Commander and select the APKs you want to install.