Amazon Prime Movie "Downton Abbey" Says My Browser Doesn't Support HD
A help page on Amazon claims Firefox can play Amazon Prime videos, yet I got a pop-up window at the beginning of the movie (not the TV series) "Downton Abbey," which I purchased in 2022, saying my browser doesn't support HD because of content. That's a paraphrase of a window that flashed on the screen and disappeared before I could take a screenshot. The window linked to a page that said Firefox browser CAN play Amazon Prime videos. So the window makes no sense to me.
Does Firefox support HD videos overall? Is there some restriction for content (whatever Amazon means by that)?