Examine source code of Youtube Theme Customizer

{
  "name": "__MSG_appName__",
  "description": "__MSG_appDesc__",
  "default_locale": "en",
  "version": "0.0.1",
  "manifest_version": 2,
  "icons": {
    "16": "logo.png",
    "32": "logo.png",
    "48": "logo.png",
    "128": "logo.png"
  },
  "permissions": [
    "storage",
    "*://*.youtube.com/*",
    "declarativeNetRequest",
    "declarativeNetRequestFeedback",
    "declarativeNetRequestWithHostAccess"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html"
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "content_scripts": [
    {
      "matches": [
        "https://youtube.com/*",
        "https://www.youtube.com/*"
      ],
      "css": [
        "content-script.css"
      ],
      "js": [
        "content-script.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{3e234bc7-deaf-46ce-9de8-6d1311cd7e1f}"
    }
  }
}