Firebase does work offline if your app loses network connectivity temporarily (details here: https://www.firebase.com/docs/web/guide/offline-capabilities...). All data written while offline is stored in memory and is synced to the Firebase servers when your client reconnects. We’re working on improving offline support when your app goes into the background, and we currently have a beta version of this available for our iOS (https://groups.google.com/d/msg/firebase-talk/dOocEtjQz4w/ss...) and Android (https://groups.google.com/d/msg/firebase-talk/gYlnLgQ-Yhk/It...) SDKs.
