Examine source code of Focus Timer is

{
  "manifest_version": 2,
  "name": "Focus Timer",
  "version": "1.0",
  "description": "A simple Pomodoro timer for productivity",
  "permissions": [
    "notifications"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{61c833c3-141f-493a-9b3e-d5ee8571ac39}"
    }
  }
}