Avoid indexing the keys in a Javascript array
You don't need to label object fields 0 or 1. On each Tab, you could have a field columns which is an array, of arrays containing the feeds in the column as so:

const Tabs = [
  {
    groupName: "News"
    columns: [
      [
        {"url":"http://xkcd.com/rss.xml","type":"mixed","limit": 8},
        {"url":"http://xkcd.com/rss.xml","type":"photo","limit": 4}
      ],
      [
        {"url":"http://xkcd.com/rss.xml","type":"mixed","limit": 8},
        {"url":"http://xkcd.com/rss.xml","type":"mixed","limit": 8},
        {"url":"http://xkcd.com/rss.xml","type":"photo","limit": 4}
      ]
    ]
  },
  {
    groupName: "Comics",
    columns: [
      [
        {"url":"http://xkcd.com/rss.xml","type":"photo","limit": 8},
        {"url":"http://superphazed.tumblr.com/rss","type":"photo","limit": 8}
      ]
    ]
  }
];