Examine source code of Open Tab Count

{
  "manifest_version": 2,
  "name": "Open Tab Count Resurrected",
  "version": "3.2resigned1",
  "description": "This extension displays the number of open tabs  for each window and the total sum.",
  "background": {
    "scripts": [
      "core/tabcount.js"
    ]
  },
  "permissions": [
    "tabs"
  ],
  "browser_action": {
    "default_icon": {
      "19": "images/folder_navy.png",
      "38": "images/folder_navy.png"
    },
    "default_title": "tab count"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "tabcount@zhegan.in"
    }
  }
}