Version: M50
OS: Windows (but probably others)

What steps will reproduce the problem?
(1) Leave calendar.google.com open for a couple of days
(2) Get multiple notifications
(3) Try to close each notification

There is no way to dismiss all notifications by calendar.google.com at once. Bug 101362 pointed to notification center to do this, but NC is gone and the user now has to close each notification separately.