I have received a lot of mails from Bugzilla yesterday.
It seems to me that Facebook is cleaning this to-be-obsolete bug reporting system (as the Bug Tool is up and running for quite a long time already). While some of the bugs are closed simply because it is “invalid” or does not have activity for a long time, there are also bug reports that are really closed (but hadn’t been updated in Bugzilla previously).
This should give me a better picture on what problems Facebook has (if someone still refer to Bugzilla for known bugs /issue).
Thanks Facebook team!