Examine source code of Popculator

{
  "manifest_version" : 2 ,
  "name" : "Popculator",
  "version" : "1.1",
  "description" : "A simple Calculator Addon for Firefox",
  "icons" : {
    "48" : "48.png",
    "96" : "96.png"
  },
  "permissions" : [
    "activeTab" 
  ],
  "browser_action" : {
    "default_icon" : "Calculator.png",
    "default_title" : "Popculator",
    "default_popup" : "index.html"
  },
  "content_scripts" : [
    {
      "matches" : [
        "<all_urls>" 
      ],
      "js" : [
        "script.js" 
      ]
    }
  ]
}