Select the Edit/Preferences or Tools/Options... menu item. Then select the Content tab as shown below.

Under the File Types section,
select the Manage... button
next to Configure how Firefox
handles certain types of files. On the Download Actions window,
enter jnlp in the Search field. The
search should locate one action as shown below.

Selection the JNLP action
and click the Change Action... button.
The Change Action window
should look like the one shown below.

If the Change Action window
contains different values, select the Open them with this application:
radio button. Then select the
Browse... button and choose the javaws application.
Some common locations for the javaws application are shown in the table
below.
| Platform |
Location |
Comment |
|---|---|---|
| Linux |
/opt/jdk1.6.0_06/bin/javaws |
System installation of Sun's JDK |
| Microsoft |
C:\Program
Files\Java\jre1.6.0_06\bin\javaws |
Installation of Sun's JRE |
| Solaris |
/usr/bin/javaws |
Default Java |
| Solaris |
/usr/jdk/instances/jdk1.6.0/bin/javaws |
Specific Java installation |