Examine source code of Simple Clock

{
  "manifest_version": 2,
  "name": "Simple Clock",
  "version": "1.0",
  "description": "Hiển thị đồng hồ trên toolbar.",
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "simple-clock@example.com"
    }
  }
}