Both of these steps are under the database section of Firebase console

NOTE: I still can't get the preview to work (show the data from Firebase)
but this resolved some data permissions issues I had in the console

1. Insert a node under your main node in the database with the name of 'todos'
and the following as the value

{'items': {1: {'title': 'finished todo', 'finished': true}, 2: {'title': 'unfinished todo', 'finished': false} }


2. Rules tab:  change the auth rules to the following - then publish changes.

{
  "rules": {
    ".read": true,
    ".write": false
  }
}