Hello everybody! This is my first posting and my poor english comes directly from a dictionary, so please be lenient... My concern:

I'm using XPSP3 + Firefox 52.9 for streaming. Until recently https://www.zdf.de/live-tv (indispensable for soccer) worked fine. Now i get the error "no format supported". VLC fails, too. I could not find out what format exactly they support, but for sure they discontinued flash. On their "not-our-problem-page" they teach me, that i need html5 and / or a new computer.

Google tells me that i need h.265 codec, so i installed x265 (wp.xin.at/x265-for-winxp-and-winxp-x64) in firefox directory - no change (how can i proof that it's working at all?).
I also tried media.player.codec.pack.plus.v4.5.5.setup.exe from chip.de. This seems to be nothing but the latest VLC for playing BlueRay files.
I did not update MediaPlayer 9 to 11, because MP is bloatware and they don't supply codecs.

Ah, not to forget: In Firefox-addons-plugins there is a standard entry "h.264 videocodec by cisco will be installed shortly". But nothing happens; probably the link is outdated. Would i need this?

I need to solve this issue by June 2022 - Soccer-World-Cup! Any hint - other than buying a TV - would be greatly appreciated!