uinstall flash player plugin using your os uninstaller and save no settings if offered. once uninstalled that dll should be removed. then install the latest fp version that suits your needs.
Sorry I did forget to mention that I am unattendant updating a lot of PCs (Win XP SP3) using install_flash_player_10_active_x.msi. This file updates the files in C:\WINDOWS\system32\Macromed\Flash\ (Flash10l.ocx, FlashUtil10l_ActiveX.dll, FlashUtil10l_ActiveX.exe etc). On some of the PCs there is also a file called NPSWF32.dll. As I understand this is used by Firefox?
But how can I update the NPSWF32.dll to the latest version running an unnattendant installation? I have found info about a file called NPSWF32_FlashUtil.exe but have not yet found from where I can download it.