This leads me to believe that Mozilla may have recently been caught up in the same spamhaus spam-trap debacle as many others and was backlisted. They decided to

This leads me to believe that Mozilla may have recently been caught up in the same spamhaus spam-trap debacle as many others and was backlisted. They decided to send a permission pass email because if an open or click hasn't recently been recorded, there isn't really any other way for them to know which emails in their list are no longer active. This also confirms my belief that one or more of the big email ISP's (yahoo, gmail, etc.) may have sold a crap load of their inactive email accounts to spamhaus recently. Doesn't matter if these once active emails did opt in to your list in the past, you will still get backlisted now that they are in the spamhaus spam-trap database. I don't understand why the email providers don't simply shut down the inactive accounts. This would then result in a hard bounce to the sender allowing them to remove the emails from their list.