Examine source code of FBLikesCounter

{
  "manifest_version": 2,
  "name": "FB LikeCounter",
  "version": "1.1resigned1",
  "description": "Show all likes on any webpage of facebook website.",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "permissions": [],
  "content_scripts": [
    {
      "matches": [
        "*://*.facebook.com/*"
      ],
      "js": [
        "CountLikesCore.js"
      ]
    }
  ],
  "applications": {
    "gecko": {
      "id": "fblikescounter@nadirlaskar.in",
      "strict_min_version": "48.0"
    }
  }
}