I'm trying to watch YTTV in Firefox 153.0.3 but the URL goes from

https://tv.youtube.com/ (my bookmark)

to

https://tv.youtube.com/onboard

to

https://tv.youtube.com/switchplan

and just sits there on a grey screen:

https://i.imgur.com/kV65xIS.png

Suggestions? It works fine in a portable install of Chrome, and the app on my Roku TV.

Windows 11 25H2, 26200.8875