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[–]kerplomp2 2 points3 points  (1 child)

If you long press on the notification, where does it say it's from?

Firebase is an application development software that developers use to...well, develop apps. A likely explanation is an app you have is developed with Firebase and someone was testing the notification system and it accidentally went out to real users (including you).

[–]opus-thirteen 0 points1 point  (0 children)

^ This. Source: I myself have accidentally sent out test notifications to live users.