Examine source code of Firefox4Dead

{
  "theme": {
    "images": {
      "theme_frame": "Header.jpg"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Firefox4Dead",
  "manifest_version": 2,
  "description": "A persona Based on Left 4 Dead's color scheme."
}