Do Not Remove Cordova, You may face some serious problem in future when you want to use some native library.
I made some tricks which solved this issue for me.
Create firebase instance just after app module like this -
var appMain = angular.module(‘starter’, [‘ngCordova’,‘ngStorage’,‘ionic’,‘starter.controllers’,‘starter.services’,‘firebase’]);
var firebaseInst = new Firebase(“https://xyz.firebaseio.com/”);
& this instance you can directly call in controller
var objMatches = $firebaseObject(firebaseInst.child(“methods”));
— Do Not Create Services for firebase instance.