Examine source code of LIGHTWORD COUNTER

{
  "manifest_version": 2,
  "name": "LIGHTWORD COUNTER",
  "author": "Olivier Tissier",
  "description": "A light and simple word counter",
  "version": "1.0.7",
  "icons": {
    "16": "images/16.png",
    "24": "images/24.png",
    "32": "images/32.png",
    "48": "images/48.png",
    "128": "images/128.png"
  },
  "browser_action": {
    "default_icon": "images/48.png",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c9d3d509-88a3-4e98-93c6-3f7bc89a52a1}"
    }
  }
}