Earlier quoted context omitted.
The DRM plugin is downloaded and installed automatically with the "normal" version of Firefox. So if you don't want to be downloading purposely-obfuscated proprietary Adobe binaries, you have to install this version. Also, by default, EME activates on any webpage that requests it.
If you disable EME (in the Firefox Preferences menu by unchecking the "Play DRM content" checkbox), Firefox will delete the Adobe CDM binary if it has been installed. https://support.mozilla.org/en-US/kb/enable-drm
Doesn't EME imply a kernel component? To safeguard the encryption keys and to generally complicate an access to the raw media? If so, does it mean that this Firefox update touches the kernel?