Examine source code of Task Timer v4

{
  "manifest_version": 2,
  "name": "Task Timer",
  "version": "1.0",
  "description": "Track your daily tasks with a simple timer",
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{c41d36cd-39ea-408c-ad1c-762fe14adba7}"
    }
  }
}