Set values of a Firebase data array using Polymer

Problem:
I want to try to have multiple games running at the root of my Firebase, they all have Firebase generated id's,
when I'm trying to fetch them using the <firebase-collection> I'm always getting an array of the Objects, and 2-way binding is very hard with Polymer.
Is there a way to get the Firebase data as an Object?

I tried to add the data-as-object attribute, but it didn't worked, I also got an array.
I even tried to use the <firebase-document> element by simply change form
<-collection> to <-document>, but then updating the game data didn't push to firebase.
I don't know if this is possible ...

Or is there a way for good two-way binding?
I can't use the index of the array item, like this: this.set('gameData.' + i), because then I'm getting the error Uncaught Error: unexpected key 2, when I try to modify the values under the Object in the array

Full code on Github

My code:
Data provider:

<firebase-collection location="https://***.firebaseio.com" 
                     data="{{data}}" data-as-object log>
</firebase-collection>
<!-- script -->
Polymer({
    is: 'tmp-game-data',
    properties: {
        data: {
            notify: true
        }
        }
});

Game Element:

<!-- map with several players(Array), -->
<!-- an player(Object) has some properties -->
<!-- on-map-ready, when the map is fully configured --> 
<tmp-map players="{{game.players}}" 
         on-map-ready="_mapReadyCallback">
</tmp-map>
<!-- menu user for creating and -->
<!-- joining games with selected settings -->
<tmp-menu on-start-global-game="startGlobalGame" 
          on-join-game="joinGame">
</tmp-menu>
<tmp-game-data data="{{gamesData}}"></tmp-game-data>
<!-- script -->
var blocks = []; //Map blocks, global access

Polymer({
    is: 'tmp-game',

    properties: {
        gamesData: {
            notify: true
        },
        game: {
            notify: true
        },
        gameId: {
            type: String
        }
    },

    startGlobalGame: function(e) {
        var gameId = getRandomString(6);
        this.set('gameId', gameId);

        var player = {id: /*playerId*/};
        var players = [player];

        this.push('gamesData', {
            gameId: gameId,
            maxPlayers: e.detail.maxPlayers,
            players: players
        });

        this.selectGame();

        //generate map
    },

    joinGame: function(e) {
        var gameId = e.detail.gameId;
        for (var i = 0; i < this.gamesData.length; i++) {
            if(this.gamesData[i].gameId === gameId) {
                var map = this.get('gamesData.' + i + '.map');
                //generate map with the map of the game
            }
        }
        this.selectGame();
    },

    selectGame: function() {
        for (var i = 0; i < this.gamesData.length; i++) {
            if(this.gamesData[i].gameId === this.gameId) {
                this.set('game', this.gamesData[i]);
                this.linkPaths('game', 'gamesData.' + i);
            }
        }
    },

    _mapReadyCallback: function(e) {
        for (var i = 0; i < this.gamesData.length; i++) {
            if(this.gamesData[i].gameId === this.gameId) {
                //get the map as a json
                var map = JSON.stringify(blocks);
                this.set('gamesData.' + i + '.map', map);
            }
        }
    }
});