Examine source code of Breath Timer

{
  "manifest_version": 2,
  "name": "Breath Timer",
  "version": "1.2.1",
  "description": "4-7-8 box and custom breathing exercise timer",
  "browser_specific_settings": {
    "gecko": {
      "id": "{33f343d8-d9a7-4f56-b721-dbc92ff51a76}",
      "strict_min_version": "96.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "icons": {
    "16": "assets/icon_16.png",
    "48": "assets/icon_48.png"
  },
  "browser_action": {
    "default_popup": "overlay/overlay.html",
    "default_icon": {
      "16": "assets/icon_16.png",
      "48": "assets/icon_48.png"
    }
  },
  "background": {
    "scripts": [
      "worker/monitor.js"
    ]
  },
  "permissions": []
}