Examine source code of hooverZoom

{
  "manifest_version": 2,
  "name": "hooverZoom",
  "version": "2.140.7.5",
  "browser_specific_settings": {
    "gecko": {
      "id": "jid1-ypAaFtWSGV9ANQ@jetpack",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "description": "A compact add-on for displaying media on mouseover.",
  "permissions": [
    "<all_urls>",
    "history",
    "storage"
  ],
  "background": {
    "scripts": [
      "main.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "all_frames": true,
      "js": [
        "mod.js"
      ],
      "css": [
        "mod.css"
      ],
      "run_at": "document_start"
    }
  ],
  "options_ui": {
    "page": "options.html"
  }
}