They could at least not intentionally block the browser and let it render to the best of its abilities. The Google Play site is still functional in desktop Fire

They could at least not intentionally block the browser and let it render to the best of its abilities. The Google Play site is still functional in desktop Firefox anyway, and it's difficult for me to imagine that it's not at least still mostly functional on Mobile Firefox. Perhaps they should inform the user that they've designed the site for a particular browser in such a case, though. A little animated GIF that says "This page works best in Google Chrome" would do the trick.