If you run optimizeit, one can observe that the native side of Java Plug-in for IE leaks memory because of incorrect handling of JNI references. Major leaks are due to sun.plugin.IExplorerPluginObject and sun.plugin.com.DispatchClient

The object sun.plugin.IExplorerPluginObject holds a reference to another big object sun.plugin.AppletViewer, therefore as you run more applets inside your browser, the amount of leak increases. This could have an impact on the scalability of the JPI.