java web start hangs when trying to start applet in browser

I'm trying to start a NASA World Wind applet in Fir开发者_StackOverflowefox. I see the spinning Java logo in the browser, however it hangs after a couple of seconds and I don't see my applet. I've been trying to enable logging but I see nothing. Things I've tried:-

set javaplugin.trace=true in deployment.properties
set TraceBasic=true and other properties in jre/bin/.javawsrc

I expected to see something under AppData/LocalLow/Sun/Java/Deployment, but I get no diagnostic messages at all.

I've placed my html, jars (signed), jnlp and required dll files in the same directory, but no applet shows up in the browser, java web start just hangs.

Any ideas for things to try or something to provoke diagnostic messages? I'm getting nothing!

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Since the Next Generation Java Plug-in Technology JWS can be used to configure applets that remain embedded in a browser page. See the Java Web Start & Applet tag information pages for more details.

Here is an example at the World Wind site. Note that the JRE reports a problem with the digital certificate, but otherwise the applet loads OK. The applet element for this applet is..

<applet id="wwjApplet" mayscript code="org.jdesktop.applet.util.JNLPAppletLauncher" width=600 height=380
      archive="applet-launcher.jar, worldwind.jar, WWJApplet.jar, http://download.java.net/media/jogl/builds/archive/jsr-231-webstart-current/jogl.jar, http://download.java.net/media/gluegen/webstart/gluegen-rt.jar">
   <param name="jnlp_href" value="WWJApplet.jnlp">
   <param name="codebase_lookup" value="false">
   <param name="subapplet.classname" value="gov.nasa.worldwind.examples.applet.WWJApplet">
   <param name="subapplet.displayname" value="WWJ Applet">
   <param name="noddraw.check" value="true">

   <param name="progressbar" value="true">
   <param name="jnlpNumExtensions" value="1">
   <param name="jnlpExtension1" value="http://download.java.net/media/jogl/builds/archive/jsr-231-webstart-current/jogl.jnlp">
</applet>

Note the first param, the jnlp_href.