A Firebase.io developer designs, builds, and maintains applications using Google's Firebase platform. They leverage Firebase's backend services like database management, authentication, cloud functions, and hosting to create scalable and secure applications. They also implement real-time data syncing for instant updates and offline support. Additionally, they use Firebase's analytics, crash reporting, and user engagement tools to monitor and improve app performance. Firebase.io developers often collaborate with front-end developers to integrate Firebase services into user interfaces. They must stay current with Firebase updates and best practices, ensuring the reliability and efficiency of the applications they develop.