Examine source code of FreeCard ext.

{
  "manifest_version": 2,
  "name": "FreeCard ext.",
  "description": "fc.city",
  "version": "1.1.16",
  "icons": {
    "128": "logo.png"
  },
  "browser_action": {
    "default_icon": "logo.png",
    "default_popup": "popup.html"
  },
  "permissions": [
    "tabs",
    "<all_urls>",
    "http://*/*",
    "https://*/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "/js/jquery.js",
        "/js/purify.js",
        "/js/contentScript.js"
      ],
      "css": [
        "/css/modal.css"
      ],
      "run_at": "document_end"
    }
  ],
  "background": {
    "page": "background.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{cdc56f98-6d49-46db-adfe-979fb98cf2e0}"
    }
  }
}