My understanding is that the react-native-firebase node module will rely on specific versions of the native Firebase libraries. Android handles this well with Gradle and version specification, but the iOS docs @ https://rnfirebase.io/docs/v4.2.x/installation/ios currently say to simply add pod 'Firebase/Core' and pod 'Firebase/Firestore', etc.
Over time, for projects that are not able to update their node modules quickly enough to keep up with breaking changes, pod 'Firebase/Firestore' (e.g.) will no longer work with old versions of the node module.
Instead, I believe the docs OR somehow the node module should specify the precise version of each Cocoapod needed (in the same way as is done on Android), e.g. pod 'Firebase/Firestore', '~> 0.11'.
Not having this is making troubleshooting an import issue very cloud for us since we cannot safely run pod update on our project.