Java Network Launch Protocol (JNLP) files are used to launch applications from a hosted web server on a remote desktop client. Software such as Java Plug-in and Java Web Start programs use JNLP files ...

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.