We know how it will impact Firefox. They will be deeply concerned with WEI and extremely opposing it, but will implement it anyway because they are forced to do it.

It’s going to go exactly like this. Again.

With most competing browsers and the content industry embracing the W3C EME WEI specification, Mozilla has little choice but to implement EME WEI as well so our users can continue to access all content they want to enjoy.

And that is almost a direct quote.