We have been seeing a similar problem. However, we also see it intermittently but not repeatably on Windows XP, using Java 1.6.0_24 and Firefox 4: sometimes everything works fine, but sometimes the applet completely fails to draw. Our applet is supplied in JAR format.

I'm not sure how much detail to add here and how much should perhaps go in a bug report, but in case it's useful to anyone: when the failure happens on the Mac, we have reports of a run time error about failing to cast a sun.plugin.dom.html.HTMLElement to an org.w3c.dom.html.HTMLAppletElement (note the different packages). The former came back from an HTMLDocument.getElementById call passing in the ID of an <applet> element, which should be returning an object from the org.w3c.dom package but by the looks of things might not be in this case.

We are having a similar problem at Tropical Fish Forum -- No Java Bubbles Appearing.

There should be an animation of water filling up right above where it says "Tropical Fish Forum" in large white letters, followed by different-sized bubbles coming up from those same three white words.

This same problem occurs on the latest version of Safari for Snow Leopard as well, although the applet works fine with Google Chrome, Opera and Omniweb on Snow Leopard.

I found a few solutions that work for me. When creating the object tag do not include a JNLP. Another option would be to, if you have a JNLP then set the separate_jvm parameter value = false <param id="separate_jvm" name="separate_jvm" value="false"/>. We have found that these two do not play well together especially when mac has a 1.6 version of the JRE installed. If you are counting on the JNLP to set a max memory size try using the parameter java_arguments parameter '<param name="java_arguments" value="-Xmx512m">', if you want to not use a JNLP but still want to launch your applet in a separate JVM. I have found that these solutions work for firefox and safari on Mac Leopard, Snow Leopard, and the soon to be released Lion