title: Error "A mutation operation was attempted on a database that did not allow mutations." when retrieving data in indexedDB
body: <p>I have this simple example code:</p>
  
  <pre><code>var request = mozIndexedDB.open('MyTestDatabase');
  request.onsuccess = function(event){
    var db = event.target.result;
    var request = db.setVersion('1.0');
    request.onsuccess = function(event){
      console.log("Success version.");
      if(!db.objectStoreNames.contains('customers')){
        console.log("Creating objectStore");
        db.createObjectStore('customers', {keyPath: 'ssn'});
      }
      var transaction = db.transaction([],  IDBTransaction.READ_WRITE, 2000);
      transaction.oncomplete = function(){
        console.log("Success transaction");
        var objectStore = transaction.objectStore('customers');
      };
    };
  };
  </code></pre>
  
  <p>I am getting this:</p>
  
  <blockquote>
    <p>A mutation operation was attempted on a database that did not allow mutations." code: "6</p>
  </blockquote>
  
  <p>on line</p>
  
  <pre><code>var objectStore = transaction.objectStore('customers');
  </code></pre>
  
  <p>Can't figure out - what do I do wrong?</p>