Examine source code of Stopwatch Popup

{
  "manifest_version": 2,
  "name": "Stopwatch Popup",
  "version": "1.0",
  "description": "A simple stopwatch (start/stop/reset) in the popup.",
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png",
    "default_title": "Stopwatch"
  },
  "permissions": [],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8e9319b4-806c-4df8-83b1-79ee649daa9b}"
    }
  }
}