Examine source code of Web Humans

{
  "description": "Both celebrate the human contribution to the Internet and encourage developers to include a credits file... This extension simply adds a link to humans.txt for the current page. The added link is unobtrusive at the top/left corner of the page and it opens to a new tab. See http://humanstxt.org/ for more info.",
  "manifest_version": 2,
  "name": "WebHumans",
  "version": "1.0.2resigned1",
  "homepage_url": "http://zesago.net/",
  "icons": {
    "48": "icons/humans-48.png"
  },
  "applications": {
    "gecko": {
      "id": "webhumans@zesago.net",
      "strict_min_version": "45.0"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "humans.js"
      ]
    }
  ]
}