var el = document.getElementsByTagName("html");
console.log(el[0].ownerDocument.defaultView.someObj);

var el = document.getElementsByTagName("html");

{
  "manifest_version": 2,
  "name": "My Ext",
  "version": "0.1",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": ["content.js"]
    }
  ],
  "browser_action": {
    "default_icon": "images/logo.svg"
  }
}