Denny has the absolute right answer. I also wanted to add, however, don't use $scope if you don't need. It adds overhead to your app that you don't need. Try the following:
var self = this;
self.settings = { };
self .post_social = function() {
var ref = new Firebase(path);
ref.update({
twitter: self.settings.twitter || '',
facebook: self.settings.facebook || '',
google: self.settings.google || ''
});
toaster.pop('success', "System", "Settings saved!");
};
Also, I highly recommend putting your toaster popups in a service. It lets you swap alert services in and out easily. It doesn't seem like a big thing, but we had a customer want a different style of messages and we were able to swap out the plugin and change the alertService and not affect any other areas of our code.