https://www.bleepingcomputer.com/news/security/mozilla-aims-to-reduce-web-site-notification-spam-in-firefox/

Mozilla is performing a study on how to reduce the increasing usage of displaying web site browser subscription prompts that users find annoying and are abused to send browser notification spam appearing on a user's desktop.

Browser notifications allow web sites to push notifications to users when they create new content. These content notifications are a useful way to increase traffic as they appear on a user's desktop, even if the user is not currently visiting the associated site.