SOLVED: Metadata 4:3 setting not being respected

[Domarius]

I have a bunch of video episodes of an old cartoon, and whoever transferred it from VHS perhaps encoded it in a 16:9 format when it should be 4:3

I used MKVToolNix to set the meta data of all the episodes to be 4:3 - these play perfectly from my computer in my media player! (Haruna, I'm on EndeavourOS)

But after uploading to the Jellyfin server, it has not worked.  The videos still play stretched width to 16:9.

[Domarius]

Ok weird thing is, on my friend's computer, the same video, watching through Jellyfin in the browser, is correctly 4:3. But when I watch that same video, it's stretched to the width of 16:9...

[Domarius]

Ok guess what - on Firefox it's stretched widescreen... on Brave it looks right. What could be the reason for this?

Edit: Sorry for consecutive posts, I was hoping someone would see it and have some idea. But I have to conclude - Firefox is just crap at rendering video and ignores metadata. Sorry for doubting Jellyfin!