title: ExtJS 4 Panel Grid using JsonStore is not loading the grid
body: <p>I am using ExtJS 4.0.7 and I am using JSON Store to load it to the Panel Grid. I am using Firefox version 16.0.2. It is very simple example, I am able to run Array grids. </p>
  
  <pre><code>Ext.onReady(function() {
  
  
  var Grid1Store = new Ext.data.JsonStore({
      root: 'users',
      fields: [ 'id', 'name', 'email' ],
      autoLoad: true,
      data: { users: [ 
        { "id": 1, "name":"John Smith", "email":"jsmith@example.com"},
        { "id": 2, "name":"Anna Smith", "email":"asmith@example.com"},
        { "id": 3, "name":"Peter Smith", "email":"psmith@example.com"},
        { "id": 4, "name":"Tom Smith", "email":"tsmith@example.com"},
        { "id": 5, "name":"Andy Smith", "email":"asmith@example.com"},
        { "id": 6, "name":"Nick Smith", "email":"nsmith@example.com"}
      ]}
    });   
  
  
   var Grid1Grid = new Ext.grid.GridPanel({
        store: Grid1Store,
        renderTo: 'grid-example',
        title: 'Target',
        width: 300,
      columns: [
        {
          id: 'name',
          header: "Name",
          sortable: true,
          dataIndex: 'name'
        },{
          id: 'email',
          header: "Email",
          sortable: true,
          dataIndex: 'email'
        }
      ]
  
  });
  
  });
  </code></pre>
  
  <p>Grid is loading and no data is displayed. It is showing a blank grid. I am not sure about the issue. Is it due to some browser compatibility issue?</p>