Examine source code of Ultima IV

{
  "theme": {
    "images": {
      "theme_frame": "firefoxheader.png"
    },
    "colors": {
      "frame": "#525252",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Ultima IV",
  "manifest_version": 2,
  "description": "A dedication to the old Ultima games."
}