Over the last few days we’ve started archiving content on www.mozilla.org. None of the content is being deleted—all archived content is available on the www-archive.mozilla.org site and can be brought back to the main site if needed. If someone goes to an archived page on the main site, they will get a 404 page that provides a link to that page on the archive site.
Due to the number of pages on the site and the lack of information about owners for much of that content, we are going to have to make some judgement calls about what to archive. We apologize for any inconvenience this causes and we are happy to work with people to fix anything that gets broken as part of this process. If you run into an issue with archived content, please open a bug.
Update: For a list of archived content, take a look at this Bonsai query of recent site activity (the archived pages have no value for the Rev column and 0/0 for the +/- column).