Do I need a source? AFAIK main Encrypted Media Extension advocates were Netflix and Google. See https://www.eff.org/deeplinks/2013/10/lowering-your-standard... and such. Google has a dominant user share of browsers, so just by supporting DRM Google already creates pressure on all browser developers to support DRM as well. But aside from that, Google is also a major (90%) funding source of Mozilla/Firefox.
