Of course they can kick any Facebook user/group off for any reason, but I suspect they would have a hard time taking any sort of legal action against a plugin (or tinted glasses) that merely changes the way a user's browser interprets the resources loaded from Facebook.

Anyway, I think it's silly for Facebook to be going after tools that make users like Facebook more, as long as they don't somehow degrade the experience for others (spamming, etc)