Examine source code of Get Facebook ID

{
  "name": "Get Facebook ID",
  "version": "1.2.10resigned1",
  "manifest_version": 2,
  "description": "Get Facebook ID for Facebook pages.",
  "browser_action": {
    "default_name": "FBID",
    "default_icon": "icon.png",
    "default_popup": "popup.html"
  },
  "icons": {
    "16": "16.png",
    "48": "48.png",
    "128": "128.png"
  },
  "permissions": [
    "activeTab",
    "*://*.facebook.com/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{71c195b0-5aad-4f45-bb02-54eb0046f4d8}"
    }
  }
}