Examine source code of Photo Time Machine

{
  "manifest_version": 2,
  "name": "Photo Time Machine",
  "version": "1.0",
  "description": "Hover over an image to view an older version from Internet Archive or cache.",
  "permissions": [
    "activeTab",
    "https://web.archive.org/"
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "Photo Time Machine",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{ccc028dd-27e5-4f1c-858a-116198af137a}"
    }
  }
}