Examine source code of Tabs Numbering

{
  "manifest_version": 2,
  "name": "Tab Numbering",
  "version": "1.0",
  "description": "Firefox add-on that numbers each tab in order to facilitate tab-switching to users who use keyboard shortcuts.\nSafe to use, no malicious code.\nYou can also check the code out youself on my github repository: https://github.com/siizx/firefox_tabs_numbering\n",
  "author": "Andrea P. from Italy - andreczw (siizx@live.it)",
  "permissions": [
    "activeTab",
    "tabs",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "48": "icons/icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{69987857-1e47-440f-bcf0-3943d2b42dc4}"
    }
  }
}