Examine source code of ProxyCheck

{
  "manifest_version": 2,
  "name": "ProxyCheck",
  "version": "3",
  "description": "By simply activating the ProxyChecker extension, you gain valuable insights into your proxy connection. The extension displays a convenient TAG on its logo, allowing you to instantly identify the proxy you are exposed to. This TAG serves as a visual indicator of the proxy's properties, helping you make informed decisions about your online activities.",
  "icons": {
    "239": "icons/proxy.png"
  },
  "permissions": [
    "http://ip-api.com/json/",
    "activeTab",
    "storage"
  ],
  "background": {
    "scripts": [
      "ipchecker.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_icon": "icons/proxy.png",
    "default_title": "ProxyCheck",
    "default_popup": "./popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "proxycheck@tmo"
    }
  }
}