Examine source code of Neopets Oldifier

{
  "description": "Changes happy, uncustomized neopets' images to their older, non-fist-clenching versions.  I made this addon because I missed the old poses, they had so much personality to them.  Now you can see them again for any neopet with an older version (so no colors created post-customization update will be eligible for a reversion obviously) who is both uncustomized and happy (so no starving neopets).  If any color/species combos are missing that DID have an older image, feel free to say so in a review with a link to the image that is missing.  Once I see it I will add it!",
  "manifest_version": 2,
  "name": "Neopet Images to Old Versions",
  "version": "1.0",
  "web_accessible_resources": [
    "images/*.gif"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.neopets.com/*"
      ],
      "js": [
        "oldify.js"
      ]
    }
  ]
}