Examine source code of Mouse Melody

{
  "manifest_version": 2,
  "name": "Mouse Melody",
  "version": "1.0",
  "description": "Turn mouse clicks into musical notes; pitch varies by horizontal position on the page.",
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{2cf89a0d-b60c-47f5-8336-79ef9b896898}"
    }
  }
}