That's what I do on my Firestick since I don't have an android phone and too lazy to send the apks from my comp -> firestick.
1) Get that Downloader program from the Amazon store.
2) Go to this website using that Downloader program:
http://aftv.hackmykodi.com/
3) Bookmark it/put it in your favorites for easy access in the future so you won't have to type that again.
4) Download the Terrarium APK through there
5) When it prompts you to install it after it finishes downloading, install.
6) Then it asks you if you want to delete the APK, delete it.
Now that I think about it though, you could probably do the same thing with the Silk Browser by going to that low graphic website on step 2.