Examine source code of Firefox - Grey

{
  "theme": {
    "images": {
      "theme_frame": "FirefoxGreytop.png"
    },
    "colors": {
      "frame": "#9e9e9e",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Firefox - Grey",
  "manifest_version": 2
}