Examine source code of Simple Timer Popup

{
  "manifest_version": 2,
  "name": "Simple Timer Popup",
  "version": "1.0",
  "description": "Start a simple countdown timer in the popup.",
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png",
    "default_title": "Simple Timer"
  },
  "permissions": [],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{78c5b8b0-9d7e-43d8-8305-1320e68d2d24}"
    }
  }
}