Examine source code of Gmail Notifier

{
  "manifest_version": 3,
  "name": "Gmail Notifier",
  "description": "Gmail Notifier on Browser",
  "version": "0.4.0",
  "icons": {
    "16": "icon/16.png",
    "32": "icon/32.png",
    "48": "icon/48.png",
    "96": "icon/96.png",
    "128": "icon/128.png"
  },
  "permissions": [
    "storage",
    "cookies",
    "alarms",
    "notifications",
    "webRequest",
    "idle",
    "contextMenus"
  ],
  "host_permissions": [
    "https://mail.google.com/**"
  ],
  "author": "rxliuli",
  "action": {
    "default_icon": {
      "16": "icon/16.png",
      "32": "icon/32.png",
      "48": "icon/48.png",
      "96": "icon/96.png",
      "128": "icon/128.png"
    },
    "default_title": "Gmail Notifier",
    "default_popup": "popup.html"
  },
  "homepage_url": "https://github.com/rxliuli/gmail-notifier",
  "browser_specific_settings": {
    "gecko": {
      "id": "gmail-notifier@rxliuli.com"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}