Examine source code of Feedstack

{
  "manifest_version": 2,
  "name": "Feedstack",
  "version": "1.0",
  "description": "Extract and manage your Substack subscription links with RSS feed generation. Easily export all your newsletter subscriptions for backup or migration.",
  "author": "Substack Tools",
  "homepage_url": "https://github.com/707/feedstack",
  "permissions": [
    "activeTab",
    "storage",
    "*://substack.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://substack.com/settings*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Feedstack"
  },
  "icons": {
    "16": "icons/icon-16.svg",
    "48": "icons/icon-48.svg",
    "128": "icons/icon-128.svg"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "venomreborn@gmail.com",
      "strict_min_version": "70.0"
    }
  }
}