Non-proxied video playback failing
Seems that some video playback is showing "No video with supported format and MIME type found".  Plays normally via standard Twitter link.  e.g.

https://nitter.net/Not_the_Bee/status/1704218550229930447
versus
https://twitter.com/Not_the_Bee/status/1704218550229930447
(Pardon the politically charged example, I couldn't find other examples quickly.)

Using fully updated Firefox browser on Xubuntu 20.04.