Examine source code of caculator

{
  "manifest_version": 2,
  "name": "calculator ver 1.0",
  "version": "1.0",
  "default_locale": "en",
  "description": "__MSG_extensionDescription__",
  "homepage_url": "https://www.facebook.com/profile.php?id=100050794371868",
  "icons": {
    "128": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "sidebar_action": {
    "default_panel": "/index.html",
    "open_at_install": false
  },
  "permissions": [
    "contextMenus"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{ec98f553-735f-478c-9c12-6deb03d5bd7c}"
    }
  }
}