Examine source code of Hover to Hear

{
  "manifest_version": 2,
  "name": "Hover to Hear",
  "version": "1.0",
  "description": "Plays short sounds when hovering over special keywords on a webpage.",
  "permissions": [
    "tabs",
    "activeTab",
    "storage",
    "tts"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "hover.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8c1bd71e-d7b1-4d0d-aeaa-833f3b474a80}"
    }
  }
}