Setting up Tor with Privoxy and Proxomitron

[Guest]

Just to make sure I have this right, in Proxomitron, I check "Use Remote Proxy" and in the External Proxy Selector box I insert 127.0.0.1:8118 and click OK. Then in Firefox, tools - options - advanced - network - settings I use HTTP Proxy 127.0.0.1 Port 8080 and leave the SSL Proxy as 127.0.0.1 port 8118 and Socks Host as 127.0.0.1 9050.
I leave Privoxy "enabled" and "Tor Enabled."

Having done all that when I try to open Firefox - google, I get a "503" message stating "This is Privoxy 3.0.6 on localhost (127.0.0.1), port 8118, enabled" followed by a box stating "Your request for http://www.google.com/ could not be fulfilled, because the connection to http://www.google.com (127.0.0.1) could not be established."

I noticed that if Tor is disabled and then re-enabled, it changes the Firefox HTTP connection back to port 8118. This is pretty frustrating.

Any idea what could be wrong?

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Here's a follow-up: I went to Torbutton preferences and changed the custom proxy setting for HTTP Proxy to 127.0.0.1 port 8080. Now the Firefox config does not change when I enable/disable/enable Tor -- it stays as 8080. New web pages open properly, but when I do a click "test settings" in the Tor preferences window, I get a ""[Javascritpt Application]" window that states "Tor proxy test: HTTP error for check.torproject.org:503" -- I do not know what that means, so I do not know if Proxomitron --> Privoxy --> Tor is working.