Browser crashes when a page instantiates and destroys java applets very quickly. Hotspot crash log is attached. See the sample script in comments to reproduce it.
When browser notifies java plugin to stop an applet, plugin is waiting on the browser main thread for Stop Acknowledgment from the applet. During the waiting period, plug-in pumps windows messages that can cause new instances of plugin been instantiated. This recursion in applet stop can cause browser crash.