Examine source code of Reading Timer Counter

{
  "manifest_version": 2,
  "name": "Reading Timer",
  "version": "1.0",
  "description": "Track how much time you spend reading on a webpage.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{be05056c-109f-423e-bb81-f98c42517eae}"
    }
  }
}