User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:66.0) Gecko/20100101 Firefox/66.0
Steps to reproduce:
Receive new email after receiving other emails that were still unseen.
The new mail notification showed the unseen emails as well
The new mail notification shows only the new mails
(Or, if this is a feature rather than a bug, e.g. for reminding people of unseen emails, the new email should at least be on top of the notification list, i.e. they should be sorted by "order received". Otherwise the new email is not even be visible in the notification due to the limited size of the notification box if there are a couple of unseen emails.)