Examine source code of Window 8 grey

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#ffffff",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Window 8 grey",
  "manifest_version": 2,
  "description": "I think the window 8 metro firefox look cool. My window 7 with aero off look weird so try making a theme that replicate the metro grey style. (Project fail)"
}