on x86_64 both i386 and x86_64 versions firefox installed

I was checking things in preparation of removing firefox.x86_64 and
installing firefox.i386 on my x86_64 machine when I discovered that
both are already installed:

$ rpm -qa --qf '%{name}-%{version}-%{arch}\n' firefox
firefox-1.5.0.7-x86_64
firefox-1.5.0.7-i386

but then also:

$ rpm -qf /usr/bin/firefox
firefox-1.5.0.7-8.fc6
firefox-1.5.0.7-8.fc6

I suspect that firefox.x86_64 gets started though I have'nt
quite discovered how yet.

What happens if I install i386 plugins?
Does some kind of magic happen to make firefox.i386 startup then.
It might be that the shell script /usr/bin/firefox produces the magic
but I am no great hero when it come to parsing shell scripts.

Or do I have to remove firefox.x86_64 first?

Alexander