browser (UMD):
<script src="https://cdn.ethers.io/lib/ethers-5.1.umd.min.js"></script>
browser (ESM):
<script type="module">
import { ethers } from "https://cdn.ethers.io/lib/ethers-5.1.esm.min.js";
</script>
CDNJS:
<script src="https://cdnjs.cloudflare.com/ajax/libs/ethers/5.5.2/ethers.umd.min.js" integrity="sha512-PtOcu3WZTldHT+VjAJdWV5ss+iGebEgc1h5olJuxUNPvKuC0VOZsk1UhNgQYi5oIyrNHhdIOw8WQMdZwBv1MyQ==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
JSDeliver:
<script src="https://cdn.jsdelivr.net/npm/ethers@5.5.2/lib/index.min.js"></script>