Is there a way to detect 32 or 64 bit browser mode?

Hi here,
I was wondering if there is a way to detect, via Javascript or other way, if a browser is running in 32 or 64 bit mode such as the new Firefox 4 or Safari on Mac. My website uses a plugin that only works in 32 bit mode, so I would like to detect when Firefox 4 or Safari are running in 64 bit mode, so I can display the proper error message.

Thank you in advance for any help!