[ComputerGuru]

No, it’s a negotiation wherein the client submits its list of supported protocols and the server chooses between them.

[icebraining]

And since FF supports both, it's YouTube which is choosing the codec, as the8472 wrote.

[pests]

And what vim_coder and ConputerGuru meant was that Firefox would present a spoofed list of supported codecs to YouTube to force selection of the higher bandwidth, lower-powered codec.

Just because Firefox technically supports a format doesn't mean it has to disclose that format to external servers for selection.

[icebraining]

Having custom behaviors for specific sites is a terrible practice. Browsers are complex enough as they are without an extra layer of hacks.

[ComputerGuru]

Who said anything about custom behavior for custom sites? A simple “on battery? X264/265 only” is what’s being discussed here.

[the8472]

That does not work because the browser that does not know how much it can reduce the presented feature-set without actually breaking the site. Some content is vpx-only.

[username223]

It seems just about the same as having custom behaviors for specific user agents. Sadly, that's how things work these days.