Internet redirection similar to host files

I was wondering if there is a program out there that redirects access to certain websites, similar to editing the host files but using two web addresses instead of having to use an IP address.
e.g. www.google.com www.facebook.com
will redirect facebook to google if used on firefox

This is just an example of course, I want to do the redirect for more then just firefox, I want it to change for absolutely any program I choose.

I don't want to have to change the host files of every computer I go onto, or change the router settings of every network I'm on.

Non-permanent changes are preferred.