First of all, let me say that I like Deezer itself. I have a subscription to it & listen to it on my android phone & also on my shield TV (android based) and it works great.
However, on Amazon fire TV the app is atrocious. When music is playing, scrolling through looking for other music causes a clear distortion in the sound. How this got past QA I don't know.
Also, you can't browse playlists that you haven't played before! Surely this should be standard stuff.
The keyboard it uses for text input is just one line of characters, so typing in anything is laborious & long-winded. The app is slow & unoptimised.
It looks like this app needs a little bit of love from the developers. It's a shame, because spotify works well on fire TV, but I'd rather use Deezer due to spotify pandering to SJW politics.