Transparency plugin to make IE or Firefox sessions translucent?

At work people use Pidgin to IM people with a translucent
window so that other people can't see that you are talking
to friends.. This window appears see-thru to anyone who
is not very close to the monitor.

Is there a plugin or client that will allow someone to surf the
web in Firefox or Internet Explorer and have a translucent
window that is hard for other people to see what you are
surfing???

Thanks,
Tom