The testGetURLOnDestroy feature that was needed for the plugins/geturlnotify-during-document-teardown.html in TestNetscapePlugin was implemented on Windows only. When that code was unified with the Mac version, the test started crashing on Leopard and Tiger. The feature has been disabled on Mac and this bug tracks reenabling it once the bug has been fixed.
Mass closing plug-in bugs, as plug-in support has been removed from WebKit. Please comment and/or reopen if this still affects WebKit in some way.