Examine source code of Caniuse popup

{
  "browser_specific_settings": {
    "gecko": {
      "id": "caniuse@wildsky.cc"
    }
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "caniuse",
    "default_popup": "https://caniuse.com/"
  },
  "description": "popup page for caniuse",
  "icons": {
    "48": "icon.png"
  },
  "manifest_version": 2,
  "name": "Caniuse-popup",
  "version": "1.0.1"
}