Examine source code of MacMilk

{
  "theme": {
    "images": {
      "theme_frame": "header.jpg"
    },
    "colors": {
      "frame": "#4a4a4a",
      "tab_background_text": "#2e2e2e"
    }
  },
  "version": "2.0",
  "name": "MacMilk",
  "manifest_version": 2,
  "description": "A way of getting rid of the ugly theme of Firefox 4 Beta for Mac"
}