see JDK-8055464, this enhancement if for the windows registration in RegFX.cpp to add registry entries:
HKCR \ jnlp \ (Default) = "URL:jnlp Protocol"
HKCR \ jnlp \ URL Protocol = ""
HKCR \ jnlp \ shell \ open \ command \ (default) = "C:\Program Files (x86)\Java\jre1.8.0_60\bin\javaws.exe" "%1"
HKCR \ jnlps \ (Default) = "URL:jnlps Protocol"
HKCR \ jnlps \ URL Protocol = ""
HKCR \ jnlps \ shell \ open \ command \ (default) = "C:\Program Files (x86)\Java\jre1.8.0_60\bin\javaws.exe" "%1"
(of course pointing to the current javaws version being installed),
and to properly remove them on uninstall (or modify to point to the latest version).
There is also likely a registry key to automatically use Java Web Start Launcher for this. When I add just the above keys, and then launch the tests in: http://oklahoma.us.oracle.com/www/tests/jnlp/test.html (in firefox), I get a dialog asking me if I want to use the Java Web Start Launcher for this, it has a always use checkbox, if checked, I will not see this dialog again. We may also want to set whatever registry key this checkbox sets.