STR: 1. On macOS 10.12, load http://www.bennish.net/web-notifications.html 2. Click "Authorize" button. 3. Click "Show" button. RESULT: Nothing happens on macOS 10.12. This notification test works correctly in Chrome on macOS 10.12 and in Firefox on macOS 10.11.

This is working correctly for me on 10.12 with Nightly.

It doesn't work for me in Firefox 49 or Nightly 52 in a new profile. Maybe I have disabled something in my system settings, but I don't see any non-default settings in the System Preferences > Notifications page. Strangely, I don't see Chrome in the list of apps using notifications. Maybe Chrome uses a different notification mechanism.

I first noticed this problem because my IRCCloud web client stopped showing notifications when people were trying to ping me on IRC.

Kit, can you take a look?

Hmm, notifications show up for me on 49.0.1 and 52.0a1 on Sierra. Chris, would you mind running this in the Browser Console and reporting if you get one? Cc["@mozilla.org/system-alerts-service;1"].getService(Ci.nsIAlertsService).showAlertNotification("https://tests.peter.sh/resources/large-cat.jpg", "Notification title", "Some text", true); Do the notifications show up in Notification Center at all?

(Chrome uses their own notification mechanism, but you can try using system notifications by flipping chrome://flags/#enable-native-notifications).

I also could not reproduce the issue on Mac 10.12, Nightly 52.0a1.

This was (my) user error. Sorry for the false alarm. I had disabled the NotificationCenter service a long time ago (because I was annoyed from other apps' notifications). I don't know why I didn't realize earlier that I wasn't receiving IRCCloud ping notifications. http://osxdaily.com/2012/08/06/disable-notification-center-remove-menu-bar-icon-os-x/