Examine source code of Popup Calendar

{
  "manifest_version": 2,
  "name": "Popup Calendar",
  "version": "311.0",
  "description": "Shows the current month in the popup.",
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "64": "icon64.png",
      "128": "icon128.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{38bb1703-7513-4eed-b527-9a14c346e89b}",
      "strict_min_version": "109.0"
    }
  },
  "icons": {
    "64": "icon64.png",
    "128": "icon128.png"
  }
}