Examine source code of Sproutly

{
  "name": "Summer to Fall",
  "manifest_version": 2,
  "version": "1.0",
  "theme": {
    "images": {
      "theme_frame": "Yellow.png"
    },
    "colors": {
      "frame": "rgba(255, 202, 70, 1)",
      "tab_background_text": "rgba(232, 112, 22, 1)",
      "toolbar": "rgba(255, 235, 145, 1)",
      "bookmark_text": "rgba(160, 182, 102, 1)",
      "toolbar_field": "rgba(255, 250, 233, 1)",
      "toolbar_field_text": "rgba(68, 84, 42, 1)",
      "tab_line": "rgba(232, 112, 22, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{bf506e9b-50f2-4dde-8a70-f6491a7a6db3}"
    }
  }
}