As of today how is first_open event being handled on app update when the previous version of the app was using Firebase?
Is new first_open event sent on the first opening of the app after the update?
As of today how is first_open event being handled on app update when the previous version of the app was using Firebase?
Is new first_open event sent on the first opening of the app after the update?
When existing users migrate to the new version of your app which includes Firebase and app update they will log as a first_open event. And so, even though they are not new users, they log as a first_open.
As per the Documentation,
the first time a user launches an app after installing or reinstalling it
This event is not triggered when a user downloads the app onto a device, but instead when he or she first uses it. To see raw download numbers, look in Google Play Developer Console or in iTunesConnect.
The first_open event triggers only once after app installation. It does not trigger again if the app is opened several times after the app is updated.
You can also check this Stackoverflow Link.