Examine source code of NoPinkPlayer

{
  "manifest_version": 2,
  "name": "NoPinkPlayer",
  "version": "1.0",
  "description": "Feel like you're going crazy while staring at that youtube progress bar? You're not the only one! Remove the distracting pink gradient from the end of the bar with one simple addon.",
  "permissions": [
    "activeTab"
  ],
  "icons": {
    "48": "icons/npp-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "NoPinkPlayer.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{186476f2-37a1-4829-8145-b0126b9d12c9}"
    }
  }
}