It appears that with certain common configurations of FireFox on Mac (also other browsers including Opera), Java applets will crash the entire browser. We had narrowed the cause down to the Java Embedding Plug-in, but were uncertain to what extent a resolution could be reached.
Research turns up this article:
In short, the fix is to disable/delete the JAI-ImageIO plug-in which is installed during the first run of OSX. This plug-in conflicts with the JEP and causes a crash. Removing is harmless unless you are running gvSIG (a geographical information system), in which case the article explains that you can run it in the classpath rather than as an extension.
1.Navigate to: User Home directory -> Library -> Java -> Extensions or if not found Macintosh HD -> System -> Library -> Java -> Extensions
rm ~/LIbrary/Java/jai_imageio.jar or rm /System/Library/Java/Extensions/jai_imageio.jar