Examine source code of grey metal

{
  "theme": {
    "images": {
      "theme_frame": "Persona4I.jpg"
    },
    "colors": {
      "frame": "#8c8c8c",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "grey metal",
  "manifest_version": 2,
  "description": "For this Firefox style I tried to make it look like grey chrome. In my opinion it looks beautiful!"
}