On Ubuntu, torbutton configures a Firefox proxy with:
- http 127.0.0.1 8118
- https 127.0.0.1 8118
- SOCKSv5 127.0.0.1 9050
If I install minefield and vidalia on TC3 and if I configure minefield to use a manual proxy using only SOCKSv5 at 127.0.0.1 port 9050, then Tor works as shown by a visit to
https://torchec.xenobite.eu. Adding manual proxies for http and https on port 8118 does not work because there is not a proxy (polipo or privoxy) listening on that port.
Thus it appears that torbutton does not work because there is no http(s) proxy on port 8118.
While Tor seems to work without a http(s) proxy, it is possible that a proxy would protect more of your personal information; I do not pretend to understand the subtleties of this situation.