Examine source code of Double Speed Preview

{
  "manifest_version": 2,
  "name": "Double Speed Preview",
  "version": "1.0",
  "description": "Hold Shift and hover over a media playback bar to preview at 2× speed for 3 seconds.",
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_action": {
    "default_title": "Double Speed Preview",
    "default_icon": "icon.png"
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{5d9e3455-7858-4fe6-8532-a4fb65d12048}"
    }
  }
}