Examine source code of Simple Calculator

{
  "name": "Simple Calculator",
  "version": "1.0",
  "description": "A simple calculator extension for Firefox",
  "manifest_version": 2,
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "popup.js"
      ]
    }
  ],
  "permissions": [
    "tabs",
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d6b1971b-4c4b-4bdd-b33e-43c93de2719f}"
    }
  }
}