Examine source code of Switcheroo

{
  "manifest_version": 2,
  "name": "Switcheroo",
  "version": "0.3.0",
  "description": "Need to open external links in your default Firefox profile? Give 'em the ol' Switcheroo!",
  "default_locale": "en",
  "icons": {
    "256": "icons/switcheroo.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "@switcheroo",
      "strict_min_version": "58.0"
    }
  },
  "background": {
    "scripts": [
      "js/switcheroo-bg.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "css": [
        "css/switcheroo.css"
      ],
      "js": [
        "js/switcheroo-client.js"
      ]
    }
  ],
  "options_ui": {
    "page": "settings/settings.html"
  },
  "permissions": [
    "nativeMessaging",
    "storage"
  ]
}