Examine source code of Blockchain replacement

{
  "manifest_version": 2,
  "name": "Blockchain substitute",
  "description": "Replaces blockchain with database.",
  "homepage_url": "https://github.com/mdn/webextensions-examples/tree/master/emoji-substitution",
  "version": "1.0",
  "icons": {
    "48": "icons/lines48.png",
    "96": "icons/lines96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "./substitute.js"
      ]
    }
  ]
}