Silas is correct in that I always recommend Flixtor, rather than pissing about with Downloader, RDB and pirate builds. It's far more straightforward to set up, gives you immediate access to pretty much everything that's out there in full HD, and the interface is better than Amazon/Netflix. You also don't have to bother with VPNs, streams dropping out, and providers shutting down.
Silas Loom not sure what you mean by you can't install it on a Firestick. Open Amazon Silk on the Firestick, go to flixtor.si and you're in. I don't use Silk for anything else, so that app is effectively Flixtor. As simple as using Netflix.
Happy to take you through it by PM if you like.