Like web push notifications and popups are two really useful features but the amount of abuse they have had to endure is amazing. Every shitty site from newspapers to reddit to facebook must show a dark screen and ask me to subscribe to web notifications before i can see anything.
Then there are hidden APIs for which no permission is needed, like trapping of the back button (where a site gains access to my browser's back button and won't let you go back) and page close button (where it shows a popup asking you to confirm you want to leave).