Core web app compatibility vs ..... "enhanced" ad blocking. MS teams and some other business tools also don't support Firefox but work fine in Chrome and Safari.
It is something the Firefox team needs to work on again. I used Firefox from when it was released until Chrome came out and mopped the floor with it. At the time Firefox became the bloated beast and went through a reset.
Unfortunately trying to have a firm stance on not implementing HVEC when they no longer had the largest market share was a bad move and they seem to be slowly back tracking on that.
Na man I have modern 4k cameras, I need a modern browser.. They have literally build chipsets around this and many standards call for h.264 or h.265. That isn't changing.
Mozilla decided over 8 years ago not to support HVEC because of patents..
https://bugzilla.mozilla.org/show_bug.cgi?id=1332136