>From my point of view Tor cannot exist without an installed and running Pivoxy.
Sure it can .. I've been doing it with Firefox and the "foxyproxy" plug-in for some time.
The main functional element that Privoxy adds is Socks v4a support (namely, the ability to pass domain names and not IP addresses). (Privoxy also adds a lot of privacy-related stuff .. but you can edit your firefox config and use things like NoScript to accomplish almost the same things).
~Mike.