Examine source code of Dial R for Reply

{
  "manifest_version": 3,
  "name": "Dial R for Reply",
  "description": "Select text and press 'r' to insert a quote.",
  "version": "1.2",
  "icons": {
    "16": "icons/16.png",
    "32": "icons/32.png",
    "48": "icons/48.png",
    "128": "icons/128.png"
  },
  "homepage_url": "https://github.com/nashbridges/dial-r-for-reply",
  "browser_specific_settings": {
    "gecko": {
      "id": "dial-r-for-reply@nashbridges.me",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "content_scripts": [
    {
      "matches": [
        "https://*.basecamp.com/*"
      ],
      "js": [
        "content-scripts/basecamp.js"
      ],
      "world": "MAIN"
    },
    {
      "matches": [
        "https://*.slack.com/*"
      ],
      "js": [
        "content-scripts/slack.js"
      ],
      "world": "MAIN"
    }
  ]
}