I currently am using a self signed cert generated through Emby itself until I can figure out how to get a Lets Encrypt cert and ultimately get that working on my server.
So when I try and connect with the official Emby Fire TV app, I cannot access the server and get an error (assuming its the common issue of the self signed certificate). However, I downloaded and installed the Android OS .apk and loaded up the android application and was able to connect to my server and accept the self signed certificate... and connect to my server no problem. The menus don't work right because it is not designed for the Fire TV, but makes me question why the FireTV app wasn't designed in the same way as it isn't a limitation by the FireTV stick in itself, its with the development of the application.