Examine source code of More Horses

{
  "name": "More Horses",
  "manifest_version": 2,
  "version": "4.0",
  "theme": {
    "images": {
      "theme_frame": "Horses2.jpg"
    },
    "colors": {
      "frame": "rgba(69, 69, 69, 1)",
      "tab_background_text": "rgba(255, 255, 255, 1)",
      "toolbar": "rgba(0, 0, 0, 0)",
      "bookmark_text": "rgba(255, 255, 255, 1)",
      "toolbar_field": "rgba(102, 96, 96, 0.06)",
      "toolbar_field_text": "rgba(255, 255, 255, 1)",
      "tab_line": "rgba(255, 255, 255, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{14fe0e5b-cd17-4ff6-b0c0-dcea90bec0ad}"
    }
  }
}