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.

The default applications your computer uses to open files can be changed if you prefer to use something ... How to Open a JNLP File. How to Open a JNLP File. Oracle's Java plug-in supports Java ...

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.