Examine source code of Relax Timer

{
  "manifest_version": 2,
  "name": "Relax Timer",
  "version": "1.0",
  "description": "Set a focus or break timer right inside Firefox with notification alerts.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "notifications",
    "storage"
  ],
  "browser_action": {
    "default_title": "Relax Timer",
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "relax-timer@hqaddon"
    }
  }
}