Examine source code of vTableCount

{
  "manifest_version": 2,
  "name": "vTableCount",
  "version": "1.2",
  "description": "Sum values in table cells / Somar valores em células de tabelas",
  "icons": {
    "48": "icons/vtablecount.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "scripts/jquery.js",
        "scripts/vtablecount.js"
      ]
    }
  ]
}