Examine source code of Calculator

{
  "manifest_version": 2,
  "name": "Calculator",
  "short_name": "Calculator",
  "description": "A simple calculator that remembers your last calculation. You can close it at any time and reopen it without losing your work.",
  "version": "1.7.4resigned1",
  "content_security_policy": "script-src 'self'; object-src 'self'",
  "icons": {
    "16": "css/icons/16x16.png",
    "24": "css/icons/24x24.png",
    "32": "css/icons/32x32.png",
    "48": "css/icons/48x48.png",
    "64": "css/icons/64x64.png",
    "96": "css/icons/96x96.png",
    "128": "css/icons/128x128.png"
  },
  "permissions": [],
  "browser_action": {
    "default_icon": {
      "19": "css/icons/19x19.png",
      "38": "css/icons/38x38.png",
      "64": "css/icons/64x64.png"
    },
    "default_popup": "index.html",
    "default_title": "Calculator"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{220cdf48-9236-44b1-8590-b95cd0d652da}"
    }
  }
}