Trying to install from my CC account on Mac OS 10.9
Quitting Safari does not, apparently, also quit "Safari Notificati'. I've searched for the app through Search and found nothing. Don't know how I'm supposed to close SafariNotificati or where to find it.
Turning off Safari Push Notifications in Notification Center
If you've said yes to a website that is using the new Push Notifications you can turn them off by going to Safari > Preferences > Notifications and press Remove on the one you want to ditch.
Also from Apple: http://support.apple.com/kb/PH11949
You need to close the program from within Activity Monitor. Go to Application > Utilities > Activity Monitor.
Click the column title "Process Name" to sort alphabetically otherwise they move around on you.
Find Safari Notification in the list, click on it.
Then click on the buttom that looks like an octagon with an X in the middle of it.
This will force the application to quit and you can then finish your installation.