Without it, any WebRTC video conferencing applications are very CPU heavy, which cripples them on laptops especially.
Here's the bug btw: https://bugzilla.mozilla.org/show_bug.cgi?id=1210727
> The GPU->GPU copy is only usable if you also have hardware accelerated composition.
I thought WebRender is implementing such compositor.
Without it, any WebRTC video conferencing applications are very CPU heavy, which cripples them on laptops especially.