Examine source code of Magic Calc

{
  "manifest_version": 2,
  "name": "Magic Calc",
  "description": "Online Calc extension",
  "version": "1.6",
  "icons": {
    "128": "logo_128.png"
  },
  "browser_action": {
    "default_icon": "logo.png",
    "default_popup": "index.html"
  },
  "permissions": [
    "activeTab"
  ]
}