When you see that Click the Arrow not sure what you will get but keep this in mind for the other way. Click allow then go up to the Address Bar and click the Icon next to the Padlock or what looks like a i on a circle. You will get basically the same window. Click the Right Hand Sideways Arrow then More Information. Click Permissions then in that list untick Receive Notifications and any thing else you want in that list. Remember that may break connection if deny everything but can always go back and make changes. Empty Cache and delete the cookies for Youtube. Restart Firefox Please let us know if this solved your issue or if need further assistance.