Develop a cross-platform mobile and web application using Flutter and React.js for an ecommerce platform that has backend in Firebase. This application contains a web app for the seller to manage his products, inventory, sales, payments and delivery wile the mobile application is for customer facing purpose. It facilitates product viewing, cart, payment, etc.

Utilize Flutter framework to build a single codebase for both iOS and Android platforms, ensuring consistency and efficiency.

Integration with Firebase for backend services including authentication, database, and cloud functions.

Seamless user experience with smooth navigation, animations, and responsive layout designs.

Integration with RESTful APIs to fetch product data, manage user profiles, and process orders.

Implementation of push notifications using Firebase Cloud Messaging to engage users and drive sales.

Offline support for browsing products and accessing previously viewed items.

Integration of in-app analytics to track user behavior and optimize the application for better performance.