Why not make is a configuration option whether to enable the DRM in Firefox? People who only want to see non-DRM content (much like people running GNU/Linux with "libre" software only) can simply disable the DRM, and the users that are not actually tech savvy won't have to resort to, say, shudders MSIE.
Isn't that what the following portion of the blog post is all about?
"As plugins today, the CDM itself will be distributed by Adobe and will not be included in Firefox. The browser will download the CDM from Adobe and activate it based on user consent."