This app was mentioned in 3 comments, with an average of 2.67 upvotes
That's why I use http://put.io . It's a paid service, but much more reliable and flexible than something like Popcorn, and has a great Android app that supports Chromecast. Totally worth the price.
Check out put.io; it's a website from whom you can stream your torrents. Although they do not have an official App (that I know of), there are a few unofficial Apps that you can look into. Like this one: https://play.google.com/store/apps/details?id=com.stevenschoen.putionew&hl=en
Yes there is.
Stevens
https://play.google.com/store/apps/details?id=com.stevenschoen.putionew
Or Vego labs
https://play.google.com/store/apps/details?id=putio.client.android
Don't know how well optimised they are for firestick but they should work