Examine source code of No Focus Spying

{
  "manifest_version": 2,
  "name": "No Focus Spying",
  "description": "Prevent sites from being able to determine whether it is visible or not.",
  "version": "0.0.2",
  "icons": {
    "48": "icon48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "all_frames": true,
      "js": [
        "noFocusSpying.js"
      ],
      "run_at": "document_start"
    }
  ],
  "browser_action": {
    "default_icon": "icon48.png",
    "default_title": "No Focus Spying",
    "default_popup": "popup.html",
    "browser_style": true
  }
}