How "safe" and separated are profiles? For example, suppose I had a "Casual Browsing" profile and a "Banking" profile. Could I have both profiles running at t

How "safe" and separated are profiles? For example, suppose I had a "Casual Browsing" profile and a "Banking" profile. Could I have both profiles running at the same time and not risk any contamination? If I were to pick up something bad in one profile, could it leak over to the other?