A .krx file is a zip. It contains a manifest.json and a krodium.json.
The krodium.json file holds an id in the form com.vendor.app, a version and a kind.
You can also upload an extension as a .xpi or a .zip. The manifest is read and checked when you upload.
One-click install of signed .krx packages inside the browser is coming. Today, people install a free extension by downloading its package and opening it in Krodium. See Install from the Store (krodium.com/help/install-from-the-store).
Full details are in the documentation at (krodium.com/developers/docs).
Still stuck? Write to [email protected].