Examine source code of Cinema Mode

{
  "theme": {
    "images": {
      "theme_frame": "Cinema.jpg"
    },
    "colors": {
      "frame": "#000000",
      "tab_background_text": "#696969"
    }
  },
  "version": "2.0",
  "name": "Cinema Mode",
  "manifest_version": 2,
  "description": "This is for making Firefox looking like a Cinema Wide movie format. That way, when your watching videos with no full-screen feature, then you wont be bothered with bright colored borders."
}