Firebase is a Google product. The Support section of the Firebase website addresses HIPAA and Business Associate Agreements, stating that Google doesn’t intend Firebase to be used for protected health information (PHI). The site goes on to state that Google makes no representations that Firebase services satisfy HIPAA requirements.
According to the website, if you are or become a business associate as defined by HIPAA, you must not use Firebase “for any purpose or in any manner involving transmitting protected health information to Google unless you have received prior written consent to such use from Google.”