Convert Unix timestamp to date

manifest.json

{
  "background": {
    "scripts": [
      "conv_timestamp.js"
    ]
  },
  "description": "Convert Unix timestamp to date",
  "icons": {
    "16": "time-16.gif",
    "32": "time-32.gif",
    "48": "time-48.gif",
    "128": "time-128.gif"
  },
  "manifest_version": 2,
  "minimum_chrome_version": "6.0.472",
  "name": "Convert Unix timestamp to date",
  "permissions": [
    "contextMenus",
    "notifications"
  ],
  "web_accessible_resources": [
    "time-48.gif"
  ],
  "update_url": "http://clients2.google.com/service/update2/crx",
  "version": "1.0"
}