Hello 
Firefox does not play some website videos. For example the videos from this GitHub issue Tab bar visual defects · Issue #100 · outfoxxed/hy3 · GitHub .
I wonder if this needs some special configuration or additional codecs to be installed. Unfortunately there is no „extra codes“ switch or something similar as an option.
Any help on that would be appreciated 
You might need the encrypted media extension in FF in order play some video. One video in the thread does play, while the others do not.
The reason that MP4 doesn’t play is that it uses YUV444. For one reason or another, most h264 decoders don’t support this relatively uncommon format, which AFAIK is just YUV without any chroma subsampling. Unfortunately, FFmpeg seems to default to it in encoding in some cases. Firefox intentionally doesn’t support this, because it would generally not work on Windows or macOS.
It may work in Chromium but MP4s like this are likely to have trouble playing back in many circumstances.
