Examine source code of Firefox L.v.Beethoven

{
  "theme": {
    "images": {
      "theme_frame": "FirefoxL.v.BEETHOVEN_header_versie4.jpg"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#0c36f0"
    }
  },
  "version": "2.0",
  "name": "Firefox L.v.Beethoven",
  "manifest_version": 2,
  "description": "Ludwig von B's portrait and the first notes from \"Fur Elise\"."
}