Examine source code of Digital-time-clock

{
  "manifest_version": 2,
  "name": "Digital Clock with Browsing Timer",
  "version": "1.2",
  "description": "Displays time, stopwatch, and lets you set time limits for browsing.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "permissions": [
    "tabs",
    "notifications"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{17895d80-33e5-4a9b-839b-a45f651af1fc}"
    }
  }
}