Don't bend here and Mozilla itself could be under threat.
DRM exists, many major content providers have shown little interest in releasing their material without a mechanism for preventing casual copying (and you can hardly blame them), and accessing multimedia downloads is an increasingly important function of the Web. Denying that reality isn't going to achieve anything useful.
As much as Mozilla might like to take a principled stand, the fact is that they aren't important enough to force this issue. If someone can't access content in Firefox, they don't not access the content, they just use another browser. The content provider still served their content, the user still watched it, and it was still DRM'd. The only practical difference is that Mozilla lost a user.
You fight the battles you can win. There is no way Mozilla could win this one.