I have an applet which loads nicely when accessed locally (both IE and Firefox).

However, when I put my webpage in a webserver (local IPlanet), it refuses to load on Firefox (but still fine on IE). I get the following error in the java console:

load: class XXX.localprinting.LocalPrintingApplet.class not found.
java.lang.ClassNotFoundException: XXX.localprinting.LocalPrintingApplet.class
    at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.io.IOException: open HTTP connection failed:https://XXX/test/XXX/localprinting/LocalPrintingApplet/class.class
    at sun.plugin2.applet.Applet2ClassLoader.getBytes(Unknown Source)
    at sun.plugin2.applet.Applet2ClassLoader.access$000(Unknown Source)
    at sun.plugin2.applet.Applet2ClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    ... 7 more
Exception: java.lang.ClassNotFoundException: XXX.localprinting.LocalPrintingApplet.class

Any idea what could explain the different behavior in the webserver? I researched the issue of "class not found" already but without finding something relevant.