Passing illegal command-line arguments to applets via the java_arguments parameter is causing the browser to hang. The reason is the introduction of the named pipe transport for the Windows platform in 6651507 and more specifically hangs in the underlying Windows APIs. It appears that the ConnectNamedPipe API, when used in blocking mode as we do, will block until the other side opens the named pipe, and if invalid command-line arguments prevent the attached JVM from starting, then we will hang forever waiting for it to connect, which it never will. Additionally, it appears that the DisconnectNamedPipe and even the CloseHandle APIs hang while a thread is stopped in ConnectNamedPipe, so it is necessary to work around this problem.