Comments 28 and 29 confirm that they don't intend to sign email (S/MIME) certs for now, and the PDF from Mozilla in comment 30 says "Mozilla Trust Bits: Website

Comments 28 and 29 confirm that they don't intend to sign email (S/MIME) certs for now, and the PDF from Mozilla in comment 30 says "Mozilla Trust Bits: Websites" and "Mozilla is no longer accepting requests to enable the Code Signing trust bit.", so I think the intent is only to sign websites for now. That sentence happens to list of four of the six standardized uses of certificates (RFC 5280 section 4.2.1.12; the other two are timestamping and OCSP responses) so I think that's just copied-and-pasted from somewhere. Somewhat poor form to copy-and-paste that if they don't mean it IMO, but it's just prose, not the technical part of the submission.