Examine source code of No Clutter - YouTube

{
  "manifest_version": 2,
  "name": "No Clutter - YouTube",
  "version": "1.0",
  "description": "Removes Youtube's intrusive \"information\" boxes.",
  "icons": {
    "48": "NCYT-48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "NCYT@syminical.sym"
    }
  },
  "browser_action": {
    "default_icon": "popup/NCYT-32.png",
    "default_title": "No Clutter YouTube",
    "default_popup": "popup/settings.html"
  },
  "background": {
    "scripts": [
      "noClutterYT.js"
    ],
    "persistent": true
  },
  "permissions": [
    "storage",
    "tabs",
    "*://*.youtube.com/*"
  ]
}