Examine source code of Senn Volume Booster

{
  "manifest_version": 2,
  "name": "Volume Booster",
  "version": "1.0",
  "description": "Boost or reduce tab volume from 0% to 600%.",
  "permissions": [
    "activeTab",
    "tabs",
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Volume Booster"
  },
  "icons": {
    "48": "icon.svg"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "senn.seless223@gmail.com",
      "strict_min_version": "58.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "web_accessible_resources": [
    "inject.js"
  ]
}