For Google, focusing on one next gen image codec is the basic reason. A perfectly reasonable decision if made by a committee of disinterested parties deciding

For Google, focusing on one next gen image codec is the basic reason. A perfectly reasonable decision if made by a committee of disinterested parties deciding the future of the web for the benefit of humanity, but a bad look when pulled by a megacorp. For Firefox, it's about hoping to get to that latter situation. They want the web to move forward in step as much as possible rather than it being some wild west where everyone just does their own thing. They've lived through that already. And it sucked. Hence the various standardisation and community interoperability measures which have radically improved the web platform over the last decade or so.