Some Firefox users noticed playback issues on YouTube for several months. These affected high resolution videos only, from 1080p and up. To make matters worse, no clear pattern could be identified.
Some videos played fine, others would stop abruptly when they ran out of buffer.
mpv? yt-dlp? mpv is a media player, kind of like VLC but more powerful and lightweight.
yt-dlp is a CLI (command line interface) tool that allows you to download youtube videos as videos, videos without audio, or just as audio files.
More powerful and lightweight than VLC? I didn’t know such things existed.