How to Disable Firefox Ad Popup

[missionimpossible]

Firefox has an annoying ad/article popup that occasionally comes up on the top right of your screen. It seems to always be new content notifications. I've tried to disable this several times but have been successful.

Any idea how this can be disabled?

 

[Willy Strong]

This doesn't sound like Firefox and more like an extension.

Update to the latest version.
Remove any funny add-on/extensions.
Install uBlock Origin add-on.