Examine source code of Emptio

{
  "manifest_version": 2,
  "name": "Emptio",
  "version": "1.6",
  "description": "Emptio is a lightweight extension that allows external web applications to scrape raw HTML.",
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "permissions": [
    "tabs",
    "*://*/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "browser_action": {
    "default_title": "Emptio",
    "default_icon": "web-reader.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{db24e1c0-c08d-467f-aab4-ca9450ca4668}"
    }
  }
}