Attempting to link a JNLP file to /bin/javaws does not seem to be possible. The browse option is no longer there. The usual "What should FireFox do with this file?" window pops up, selecting the "Open with" Dropdown menu contains "Firefox (default)" and "Other". Select Other and you get a new window: "Select Application" where "Choose Helper Application" is empty "No applications found for "JNLP file" files", select one of "View All Applications" or "Find New Applications". Someone has tied this lookup to the same list of applications that the O/S shows in the Desktop Activities -> Applications window. This seems very wrong and limiting when the applications you wish to link are not in that list.

Firefox 48.0.1, Fedora 24, Gnome, latest release, fully patched as of yesterday.