Why isn't moving my mouse over notifications turning off the icon at the top of the screen?

[ƪilyWhite ♡]

On my Facebook account before, every time a notification came up in the corner and the icon at the top turned red, I would simply hover my mouse over the notification and the icon would go back to normal. But now, it doesn't and I have to click the notifications button at the top of the screen in order to turn the icon back to normal. Did I accidentally change something? How do I make the icon return to normal by hovering over the notification?

Thanks!