Examine source code of Simple Calculator

{
  "browser_action": {
    "default_icon": "images/icon.png",
    "default_popup": "calculator.html",
    "default_title": "Simple Calculator"
  },
  "description": "A simple calculator extension for Firefox, designed to help you make quick and efficient calculations on the fly.",
  "manifest_version": 2,
  "name": "Simple Calculator",
  "sandbox": {
    "pages": [
      "sandbox.html"
    ]
  },
  "version": "2.0"
}