Examine source code of Dark Symbols

{
  "theme": {
    "images": {
      "theme_frame": "firefoxskin-top-9.jpg"
    },
    "colors": {
      "frame": "#ffffff",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Dark Symbols",
  "manifest_version": 2,
  "description": "A great skin with a black background covered in semi-transparent grey/white/blue symbols. The artwork is mostly graffiti style and includes musical references, among other things. Enjoy!"
}