Hi

Thank you for helping to test the Nightly build of Firefox.

Please appreciate that the Nightly build is still very much "under construction" and may have unresolved issues. Does the problem occur in the main Release build of Firefox?

Release build also has this problem, but everything works in Chromium.

Are you able to provide an English translation of the two error messages?

Do you have a link to the video that you are trying to view?

"You cannot play videos in this browser" "This video is unavailable or not supported in this browser. (Error #4000)"

The problem solved by installing ffmpeg4.4 from repository

Streaming issues on Nightly are pretty common since it’s a testing build. You can try disabling hardware acceleration, testing with a clean profile, or switching temporarily to the stable Firefox release to confirm it’s not an OS-level issue. Also make sure all codecs are installed on CachyOS, since missing media packages can break YouTube and Twitch playback.