Option 1) Stick to your laurels and refuse to implement DRM. Other browser vendors implement DRM, certain parts of the web become inaccessible via Firefox as DRM is implemented into more and more web services (think Youtube, Vimeo, Netflix, Hulu). Firefox's lack of DRM means its users are being disadvantaged.
Option 2) Implement DRM. Accept temporary defeat, don't lose browser share to Chrome and continue fighting from within against DRM.
Which option do you think sounds more appealing to Mozilla? Die on your sword, keep the trust of your dwindling user base or implement DRM and retain most of your user base (minus the people that will leave because of this decision). I think someone needs to create a fork and build a DRM-less browser, that's the beautiful thing about open source, don't like something, change it.