We have seen some application crashes reported when the AppDynamics iOS Agent is used with an application already using Google Firebase. The related issues have to do with a possible race condition that occurs with overlapping method swizzling between our agent and Firebase during initialization.
Another option is to disable the auto-instrumentation in the iOS Agent (as described in enableAutoInstrument). However, doing this in the iOS Agent would remove a lot of functionality, including auto instrumentation of network requests and system and UI events. You would still retain crash handling, custom metrics, and screenshots.