Tor browser's video player often stops buffering early when it has buffered very little data, then it does not resume buffering early enough when the buffer nears empty. If it runs out of buffer and starts displaying the animated dots, it does not let you resume playback until there is quite a lot of newly buffered data and you have to wait for a long time. Even if you seek back to a position that is already downloaded it does not immediately resume.

P61714
It is often much faster to download the whole video into a file and watch it in a media player.

Web browsers playing video and audio files was a mistake.
Running scripts was also a mistake.
The convenience of... misusing a web browser like it's a video player!?
"cat -v considered harmful" but nobody bats an eye at Firefox opening anything and everything.

use yt-dlp

firefox has been that way since the introduction of html 5. never tried chrome

P61714
If you are serious about security, download your common purpose file with curl or yt-dlp, get a networkless qube (QubesOS) or a networkless video player with pledge (OpenBSD).
P61720
Web browsers doing anything but downloading and rendering web pages was a mistake.