The World Wide Web Consortium (W3C), once the force for open standards that kept browsers from locking publishers to their proprietary capabilities, has changed its mission. Since 2013, the organization has provided a forum where today's dominant browser companies and the dominant entertainment companies can collaborate on a system to let our browsers control our behavior, rather than the other way.
This system, "Encrypted Media Extensions" (EME) uses standards-defined code to funnel video into a proprietary container called a "Content Decryption Module." For a new browser to support this new video streaming standard -- which major studios and cable operators are pushing for -- it would have to convince those entertainment companies or one of their partners to let them have a CDM, or this part of the "open" Web would not display in their new browser.
This is the opposite of every W3C standard to date: once, all you needed to do to render content sent by a server was follow the standard, not get permission. If browsers had needed permission to render a page at the launch of Mozilla, the publishers would have frozen out this new, pop-up-blocking upstart. Kiss Firefox goodbye, in other words.