This bug is related to mozilla bugzilla bug: https://bugzilla.mozilla.org/show_bug.cgi?id=291522. The test case: https://bugzilla.mozilla.org/attachment.cgi?id=181581.

The test case is written in a special way. As the comment(https://bugzilla.mozilla.org/show_bug.cgi?id=291522#c4) states, "archive" is specified with a https link: https://bugzilla.mozilla.org/attachment.cgi?id=181574.

If I download the test case to a local directory and change the "archive" to a local jar file, it works well. But the test case on the web can hang my Firefox on Solaris snv_54. There are some error output in the Java console:

load: class JavaScriptApplet.class not found.
java.lang.ClassNotFoundException: JavaScriptApplet.class
   at sun.applet.AppletClassLoader.findClass(AppletClassLoader.java:183)
   at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
   at sun.applet.AppletClassLoader.loadClass(AppletClassLoader.java:127)
   at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
   at sun.applet.AppletClassLoader.loadCode(AppletClassLoader.java:626)
   at sun.applet.AppletPanel.createApplet(AppletPanel.java:778)
   at sun.plugin.AppletViewer.createApplet(AppletViewer.java:2028)
   at sun.applet.AppletPanel.runLoader(AppletPanel.java:707)
   at sun.applet.AppletPanel.run(AppletPanel.java:361)
   at java.lang.Thread.run(Thread.java:619)
Caused by: java.io.IOException: open HTTP connection failed.
   at sun.applet.AppletClassLoader.getBytes(AppletClassLoader.java:286)
   at sun.applet.AppletClassLoader.access$100(AppletClassLoader.java:44)
   at sun.applet.AppletClassLoader$1.run(AppletClassLoader.java:173)
   at java.security.AccessController.doPrivileged(Native Method)
   at sun.applet.AppletClassLoader.findClass(AppletClassLoader.java:170)
   ... 9 more

A dialog also shows that the web site's certificate cannot be verified. (Name: bugzilla.mozilla.org).

I've also met some other similar situation. If the class file specified by "code" in html file can't be found, Firefox also hangs.
I could not access the testcase from bugzilla by some reason.
A recent fix for JPI solaris/linux may address this problem (see bug 6521732).
Alfred, can you please re-attach the testcase here with this bug or contact me so that I can send you a build image with fix 6521732 to verify.
Thanks.