It seems like both that and "Introducing a new referrer tracking protection in Strict Tracking Protection and Private Browsing" link to blog posts that are supposed to exist but maybe haven't been switched to "published" status?
Maybe they will show up eventually in the list of security-related blog posts? https://blog.mozilla.org/security/category/security/
EDIT: Looks like that link works now
Re:Firefox 93
by wisniewskit on Tuesday October 05, 2021 @10:56AM
(#28760353)
The post was finally just published, the link should work now.
https://blog.mozilla.org/security/2021/10/05/firefox-93-feat...