Firebase is a set of tools and services proposed by Google, not only for Android but also for other environments. It contains products like Real Time Database, Authentication, Analytics etc.
Google has some detailed guidelines to setup Firebase for Android and enumerates the libraries required to be deployed for each service. Some of those libraries have a dependency on Google Play Services, some others don't. For instance Crashlytics, a very useful library to monitor application stability and report crashes does not require the Google Play Services to be installed in the device. However the Analytics library does require Google Play Services.
Do not hesitate to contact Famoco Support team to verify if a specific Firebase library requires the Google Play Services.