Firefox on Chromecast(Android TV) weird bug

So I know the android TV version is discontinued, but I love Firefox, so I manage to side-loaded the general android version in it... The installation is successful, and the app boots up as normal as it is on my phone, but then I notice something weird, browsing area is covered in some sort of "grey transparent overlay"(First image) and I can't even browse the content. Strangely, I think the web itself is working properly, I can click on stuffs, and when I switch to tab views or screenshot(2&3 image), they actually showed normally... It's just some unknown visual grey covering???? I understand side-loading is kind of "illegal", but it really makes me vomit just imagine chrome browser staying on my Chromecast, please, if anyone know what might be causing this...