Examine source code of Volume Booster 1200%

{
  "manifest_version": 2,
  "name": "Volume Booster 1200%",
  "version": "1.0",
  "description": "Boost audio volume up to 1200%",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Volume Booster 1200%"
  },
  "icons": {
    "48": "icon-48.png",
    "96": "icon-96.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{983183ef-1a94-48fc-aca4-5f6499ff31b8}"
    }
  }
}