I hit a few snags while trying to get this site set up with Google Analytics 4, so I’m just noting them down here in case it helps someone else who’s scratching their head and searching all combinations of ‘firebase web app ga4 enhanced measurement’ and coming up with nothing.
It’s very easy to set up Firebase Analytics as a datastream into GA4 but: it does not seem to allow for enhanced measurement. The option to turn that on is within the GA admin interface, and that is not interactable when the stream has been set up from Firebase. There doesn’t seem to be anything in the Firebase UI or documentation either, so I’m assuming it’s just not possible at this point.
Another slight mismatch between the two platforms is that once you link a datastream from Firebase you cannot see the measurement ID in GA - you need to dig it out from the SDK config in Firebase project settings. You shouldn’t really need it if you do all the tracking from Firebase, but that’s where to find it if you do.
Also worth noting that once you have a GTM datastream set up you cannot link Firebase into the same stream; it has to be a separate one, though it can be in the same property. Seems to me like a recipe for duplication but there may well be use cases I haven’t considered.
In my case, as it’s just a static website, it makes most sense to stick with GTM for all the tracking. I could do with the practice with tags anyway, and I get my nice enhanced measurement: