Examine source code of Better Trello

{
  "manifest_version": 3,
  "version": "1.9",
  "name": "Better Trello",
  "permissions": [
    "activeTab",
    "storage",
    "webRequest"
  ],
  "host_permissions": [
    "https://trello.com/*",
    "https://app.butlerfortrello.com/*"
  ],
  "description": "Better Trello is a browser extension that enhances the Trello experience.",
  "action": {
    "default_popup": "action/default_popup.html",
    "default_title": "Better Trello"
  },
  "background": {
    "scripts": [
      "./background/scripts.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://trello.com/*"
      ],
      "js": [
        "content_scripts/content-0.js"
      ],
      "css": [
        "content_scripts/content-0.css"
      ]
    }
  ],
  "icons": {
    "16": "icons/icon_16.png",
    "48": "icons/icon_48.png",
    "128": "icons/icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{dbfb9b3b-0d82-4f43-989e-85d3bbf714de}"
    }
  },
  "web_accessible_resources": [
    {
      "resources": [],
      "matches": [
        "https://trello.com/*"
      ]
    }
  ]
}