I read the OP as saying he wants two or more user accounts and he wants different default browsers fort the accounts.
Yes, he can do that. The piratical limit is the different kinds of browsers available.
here is a abridged t list:http://download.cnet.com/mac/browsers/most-popular/3101-2137_4-0.html
That makes seven. Don't known why ignored SeaMonkey.
Also, even one browser will kept different favorites for each user anyway. Some browsers allow customization, which nalso can nbe different for each user.
Of course, you can't run two users are the same time with each his own keyboard. Doesn't work that way. No yet.Oops. Yes, you can on a Mac.