angularfire, callback on retrieved data

I want to call a function once I get my firebase data back, however, I don't see any promises function like then on the ref object. Any suggestion? Here is my code:

angular.module('myMod', ['firebase']).controller('myCtrl', ['$scope', '$firebase',
    function($scope, $firebase) {
        var ref = new Firebase('myfirebaseurl');

        $scope.data = $firebase(ref);

        // i want to do something like
        data.then(function(){
           someFunc();
        });

        // or something like
        $scope.$watch('data', function(){
            if($scope.data.desiredProperty) {
              doSomething();
            }
        });
    }]);