Unpopular opinion, perhaps - isn't this just tech looking for a problem to solve?
The fact that the apps I would actually care about having on real estate on my front room seem to be nowhere to be seen is kinda glaring from my perspective... I know there's a certain purism to having Firefox front and center... But really?
Firefox, and airmouse, and an adblocker are the main tools to free yourself from commercial streaming services.
I'd argue that that's orthogonal; this is making the general UI work well on a TV, then apps get populated into that. And honestly I'll bet that for most uses Firefox working well is what you want, since a handful of shortcuts to open Firefox to assorted streaming services would do the trick quite nicely.