What is the actual difference between GA4 and Firebase Analytics, and which should own app events?
Quick answer
There is no separate 'Firebase Analytics' product anymore in the sense of a competing analytics engine - Firebase Analytics is the app-side SDK and event pipeline that feeds directly into a GA4 property, using the same event model, the same reporting backend, and the same BigQuery export format as GA4's web tracking. The real question isn't which tool should own app events, it's whether you're looking at that data through the Firebase console or the Analytics (GA4) console, and how you unify it with web data in one GA4 property.
Why This Happens
Historically, Firebase Analytics and Google Analytics were separate products with separate data models. When Google rebuilt Analytics around the event-based schema originally designed for Firebase (that rebuild became GA4), it merged the two: a GA4 property for a mobile app is, under the hood, powered by the Firebase SDK, and a GA4 property that also tracks a website uses the web gtag.js/GTM path - both feeding the same property and the same underlying event schema.
This is why app developers still see a 'Firebase Analytics' label inside the Firebase console: it's a convenience view scoped to app-specific configuration (like Cloud Messaging integration or Crashlytics correlation) layered on top of the same GA4 property, not a second, independent measurement system collecting different data.
Fix It
Confirm your app and web properties are linked (or intentionally separate)
In GA4 Admin > Data Streams, check whether your app data stream and web data stream sit under the same property. If you want a single cross-platform view of a user's journey across app and web, they need to be the same GA4 property, not separate ones.
Use the Firebase SDK for app-side event collection, not a manual Measurement Protocol integration
For mobile apps, the Firebase SDK (or the Firebase Analytics for Unity/Flutter equivalents) is the supported, automatically-instrumented path - it handles session management, user properties, and app-specific automatic events (first_open, app_update, etc.) correctly. Hand-rolling app events via raw Measurement Protocol calls loses this automatic instrumentation.
Decide where configuration actually happens
Custom dimensions, audiences, and conversion (key event) marking are configured once, in the GA4 Admin interface, and apply across whichever data streams (app and/or web) sit in that property - there's no separate configuration surface specific to 'Firebase Analytics' that needs to be kept in sync.
How To Verify It Worked
In GA4 Admin > Data Streams, confirm both your app and web streams (if you have both) list under the same Property ID at the top of the Admin panel - that single property ID is the actual source of truth for whether app and web are unified.
In DebugView, trigger an event from the app (using Firebase's debug mode, e.g. enabling debug mode via ADB on Android or the Xcode scheme argument on iOS) and confirm it appears in the same DebugView stream as your web events, tagged with the correct platform, which confirms both are landing in one property rather than two disconnected ones.
Still Not Fixed?
We audit and fix GA4 implementations for a living - if this doesn't resolve it, the next step is usually a full event-by-event audit.
Talk to a GA4 Consultant