I noticed a similar crash on MacOSX when you accept the cerfiticate temporarily. it would cause a crash on the second run in the same place (switch applet) when it checks the certificate of the downloaded jars it somehow conflicted with the first cerftificate check. I fixed it by creating a minimum delay between the first certficate accept prompt and the switch applet method.
edit:
I set the delay to the first time check plus 1000 milliseconds
Also the applet example doesn contain "<param name="separate_jvm" value="true">" this may help prevent at least the browser crashing (otherwise it kills firefox even when closing the browser window).
edit2:
after testing the applet using no cache, and running in a seperate vm, it seems that it really is a problem with multiple certificates, strange that no exception is thrown. I doubt it can be fixed short of making sure correct certificates are used.