Examine source code of YouTube Thumbnail Viewer

{
  "manifest_version": 2,
  "name": "thumbnailViewer",
  "version": "1.4",
  "description": "Displays Youtube Thumbnail",
  "browser_specific_settings": {
    "gecko": {
      "id": "titan@owo.help",
      "strict_min_version": "68.0"
    }
  },
  "background": {
    "scripts": [
      "thumbnailViewer.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "16": "icons/icon.png"
    }
  },
  "permissions": [
    "activeTab"
  ]
}