When the mozilla.* newsgroups were originally set up, they were fed to Google Groups for archival purposes. Google allowed read-only access, not allowing posting via Google.
Things have changed (purposely). You can now use Google Groups to post to the mozilla.* newsgroups, and those posts will be fed to news.mozilla.org.
Anyone wishing to use Google Groups to post to the mozilla.* newsgroups, PLEASE read these: