Examine source code of Just Arrived

{
  "name": "Just Arrived",
  "version": "1.3",
  "description": "An extension that helps differentiate read & unread tweets",
  "manifest_version": 2,
  "permissions": [
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://twitter.com/home",
        "https://twitter.com/"
      ],
      "js": [
        "contentScript.js"
      ]
    }
  ],
  "icons": {
    "16": "icons/logo_16.png",
    "32": "icons/logo_32.png",
    "48": "icons/logo_48.png",
    "128": "icons/logo_128.png"
  }
}