Bug 897874 - [Notification] horizontally scrollable with many CB message...

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Bug 897874 - [Notification] horizontally scrollable with many CB messages
https://bugzilla.mozilla.org/show_bug.cgi?id=897874

The problem was the notification items that were added by cell_broadcast_system.js have notificationID being undefined. And somehow the notificationNode.dataset.notificationID value is 'undefined' string value.