In the end, in Firefox went to Edit--> Preference-->Applications then scrolled down to the JNLP file extension and picked "Use other..." from the drop down menu. Then found javaws from the relevant directory.
In the end, in Firefox went to Edit--> Preference-->Applications then scrolled down to the JNLP file extension and picked "Use other..." from the drop down menu. Then found javaws from the relevant directory.