Examine source code of NPM Files Explorer

{
  "manifest_version": 2,
  "name": "NPM Files Explorer",
  "version": "1.0.0",
  "description": "Adds a button to browse files of a package on NPM",
  "icons": {
    "16": "icon.png",
    "48": "icon.png",
    "128": "icon.png"
  },
  "content_scripts": [
    {
      "css": [
        "button.css"
      ],
      "js": [
        "content.js"
      ],
      "matches": [
        "https://www.npmjs.com/package/*"
      ]
    }
  ]
}