The Mozilla Foundation restricts distribution of packages with their
trademarks.  See the following URLs:

  http://www.mozilla.org/foundation/trademarks/
  http://www.mozilla.org/foundation/trademarks/distribution-policy.html
  http://www.mozilla.org/foundation/trademarks/faq.html

If you want a 100% free and redistributable package, you can disable the
official-mozilla-branding option to get a non-trademarked build.