Examine source code of No Twitter Crop

{
  "name": "No Twitter Crop",
  "description": "Get rid of Twitter's image crop on single image tweets.",
  "version": "1.1a",
  "manifest_version": 2,
  "browser_action": {
    "default_popup": "popup.html"
  },
  "icons": {
    "16": "/images/notwittercrop16.png",
    "32": "/images/notwittercrop32.png",
    "48": "/images/notwittercrop48.png",
    "128": "/images/notwittercrop128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://*.twitter.com/*"
      ],
      "css": [
        "twitter.css"
      ]
    }
  ]
}