Examine source code of Compendium for DnD 5e

{
  "manifest_version": 3,
  "name": "Compendium for DnD 5e",
  "description": "A 5e compendium for easy access to spells, rules, items, and more while playing a game online",
  "version": "1.0",
  "permissions": [
    "activeTab"
  ],
  "host_permissions": [
    "https://www.dnd5eapi.co/"
  ],
  "action": {
    "default_popup": "src/popup.html",
    "default_icon": {
      "128": "icons/128d20.png"
    }
  },
  "icons": {
    "48": "icons/48d20.png",
    "128": "icons/128d20.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "manifest@v3.com"
    }
  }
}