Examine source code of Bell icon

{
  "manifest_version": 2,
  "name": "Bell icon",
  "version": "1.0",
  "description": "The bell icon is often used when there are unread notifications, the bell icon usually shows a red dot or the number of notifications.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html",
    "default_title": "Click me!"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{1ffacaa9-22a2-4ab6-93da-80406463c392}"
    }
  }
}