Examine source code of Simple Timer Addon

{
  "manifest_version": 2,
  "name": "Timer Addon",
  "version": "1.0",
  "description": "A simple timer addon for Firefox.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{6ce6e056-5689-42aa-a7be-0c09c502947a}"
    }
  }
}