I've been using Ubuntu for a while and Java Web Start applications have never "just worked" in the current or any prior version, so I ignored them until now. However, now I have a need to get them working in Firefox. When I am on a page like this: http://www.oracle.com/technetwork/java/demos-nojavascript-137100.html I want to be able to click on the demos as suggested and have them run.

I'm running Ubuntu 11.10 with Gnome 3 and/or Linux Mint 12 (64 bit) with OpenJDK 6, OpenJDK 7 and Sun Java 6. My default is currently: /usr/lib/jvm/java-6-openjdk/jre/bin/java

$ whereis javaws
javaws: /usr/bin/javaws

/etc/alternatives/javaws -> /usr/lib/jvm/java-6-openjdk/jre/bin/javaws

Here's the error I get when I try to run a Java Web Start application:

net.sourceforge.jnlp.LaunchException: Fatal: Initialization Error: Could not initialize application.
    at net.sourceforge.jnlp.Launcher.createApplication(Launcher.java:776)
    at net.sourceforge.jnlp.Launcher.launchApplication(Launcher.java:552)
    at net.sourceforge.jnlp.Launcher$TgThread.run(Launcher.java:887)
Caused by: net.sourceforge.jnlp.LaunchException: Fatal: Initialization Error: A fatal error occurred while trying to verify jars.
    at net.sourceforge.jnlp.runtime.JNLPClassLoader.initializeResources(JNLPClassLoader.java:448)
    at net.sourceforge.jnlp.runtime.JNLPClassLoader.<init>(JNLPClassLoader.java:176)
    at net.sourceforge.jnlp.runtime.JNLPClassLoader.getInstance(JNLPClassLoader.java:295)
    at net.sourceforge.jnlp.Launcher.createApplication(Launcher.java:767)
    ... 2 more
Caused by: 
net.sourceforge.jnlp.LaunchException: Fatal: Initialization Error: A fatal error occurred while trying to verify jars.
    at net.sourceforge.jnlp.runtime.JNLPClassLoader.initializeResources(JNLPClassLoader.java:448)
    at net.sourceforge.jnlp.runtime.JNLPClassLoader.<init>(JNLPClassLoader.java:176)
    at net.sourceforge.jnlp.runtime.JNLPClassLoader.getInstance(JNLPClassLoader.java:295)
    at net.sourceforge.jnlp.Launcher.createApplication(Launcher.java:767)
    at net.sourceforge.jnlp.Launcher.launchApplication(Launcher.java:552)
    at net.sourceforge.jnlp.Launcher$TgThread.run(Launcher.java:887)

Here's another example:

http://docs.oracle.com/javase/tutorial/uiswing/events/keylistener.html

net.sourceforge.jnlp.LaunchException: Fatal: Read Error: Could not read or parse the JNLP file.
    at net.sourceforge.jnlp.Launcher.fromUrl(Launcher.java:491)
    at net.sourceforge.jnlp.Launcher.launch(Launcher.java:283)
    at net.sourceforge.jnlp.runtime.Boot.run(Boot.java:199)
    at net.sourceforge.jnlp.runtime.Boot.run(Boot.java:51)
    at java.security.AccessController.doPrivileged(Native Method)
    at net.sourceforge.jnlp.runtime.Boot.main(Boot.java:165)
Caused by: java.io.IOException: port out of range:-2147483648
    at net.sourceforge.jnlp.JNLPFile.openURL(JNLPFile.java:255)
    at net.sourceforge.jnlp.JNLPFile.<init>(JNLPFile.java:185)
    at net.sourceforge.jnlp.JNLPFile.<init>(JNLPFile.java:162)
    at net.sourceforge.jnlp.JNLPFile.<init>(JNLPFile.java:148)
    at net.sourceforge.jnlp.Launcher.fromUrl(Launcher.java:477)
    ... 5 more
Caused by: 
java.io.IOException: port out of range:-2147483648
    at net.sourceforge.jnlp.JNLPFile.openURL(JNLPFile.java:255)
    at net.sourceforge.jnlp.JNLPFile.<init>(JNLPFile.java:185)
    at net.sourceforge.jnlp.JNLPFile.<init>(JNLPFile.java:162)
    at net.sourceforge.jnlp.JNLPFile.<init>(JNLPFile.java:148)
    at net.sourceforge.jnlp.Launcher.fromUrl(Launcher.java:477)
    at net.sourceforge.jnlp.Launcher.launch(Launcher.java:283)
    at net.sourceforge.jnlp.runtime.Boot.run(Boot.java:199)
    at net.sourceforge.jnlp.runtime.Boot.run(Boot.java:51)
    at java.security.AccessController.doPrivileged(Native Method)
    at net.sourceforge.jnlp.runtime.Boot.main(Boot.java:165)