According to the lawsuit, Facebook and a number of its services including Instagram, WhatsApp and Facebook Messenger all make use of patent - protected technology created by BlackBerry, including displaying a count of unread messages on a notification bubble. (ibtimes.com)
If you enable it, you'll get a count of unread messages in the tab as shown below. (neowin.net)
Keeping up with a garbage fire of unread emails on the... (bustle.com)