this is a regression created by a fix in 6u1 b01:

*6464971*: Need to implement webstart/plugin part of the bug fix 6439864

The code resets that handler for every app, instead of setting it up statically when plugin is initialized.

2 problems:

1. the following exception is shown when you load another applet with the current plugin instance

java.lang.IllegalStateException: DesktopBrowse instance has already been set.
    at sun.awt.DesktopBrowse.setInstance(Unknown Source)
    at sun.plugin.AppletViewer.setAppletContext(Unknown Source)
    at sun.plugin.viewer.IExplorerPluginObject.<init>(Unknown Source)
    at sun.plugin.viewer.IExplorerPluginContext.createPluginObject(Unknown Source)

2. Desktop.browse only works for the first applet loaded; subsequent applet calling Desktop.browse won't work, and will result in a NullPointerException.