Since JNLP files are simply Java Web Start files that open applications through an Internet browser, any browser that works in Windows 8.1 will open a JNLP file as long as you have Java installed.

Double-click JPadFX.jnlp from a file manager program to run JPadFX via Java Web Start. Similarly, double-click JPadFX.html to load this HTML file in a browser and run the application in that ...

Like Java applets, your application will be constrained to a sandbox on the client unless you used signed jars and configure permissions correctly in your application's JNLP file.