Examine source code of Black Squares

{
  "theme": {
    "images": {
      "theme_frame": "blacktop.png"
    },
    "colors": {
      "frame": "#000000",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Black Squares",
  "manifest_version": 2,
  "description": "See the black squares in your Firefox browser!"
}