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.

Opening the JNLP file initiates the Java Web Start client, which processes the JNLP file. Java Web Start downloads the entire application if the application was not previously downloaded.

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.