JART  Sorry for the late response. It seems there is no way to get notifications when a comment is posted.

About your problem: the scenario you describe doesn't require messing with config files. Just create a network location for Tor, specify localhost:9050 as SOCKS proxy, and make sure it works. Then you just re-install BFilter and it will create a "(BF) Tor" location, which will work as you want:

Browser -> BFilter -> Tor -> Internet.

Editing the forwarding.xml file is only necessary if you want to have more than one chain between BFilter and the Internet.

Note that on OSX, an entry in forwarding.xml overrides a network location of the same name. But again, you don't need modifying forwarding.xml for your scenario to work.  
(Version 1.0.9)

JART  Because the Mac version doesn't have a GUI, it's a little tricky. You have to edit the following file:

/Library/Application Support/BFilter/config

and add "page_cleanup = safe" (without quotes) somewhere after "ad_border = none". If you didn't have an earlier version installed, then you edit the option, not add it.

The possible values are "off", "safe" and "maximum".

They are documented here:

http://svn.sourceforge.net/viewvc/bfilter/trunk/bfilter/conf/config.default?view=markup

Finally, you have to restart BFilter. Either just reboot, or issue this command from the terminal:

sudo /Library/StartupItems/BFilter/BFilter restart  
(Version 1.0.6)

JART  When BFilter is installed, it duplicates your network locations, like this:

Automatic

(BF) Automatic

Suppose "(BF) Automatic" is selected. In this case, BFilter finds the counterpart location "Automatic", to check if it needs to use an upstream proxy.

The error you are getting means that "(BF) Automatic" uses a network interface (AirPort, Ethernet, ...) that's not configured in "Automatic".

If reinstalling BFilter doesn't help, try uninstalling it, then make sure your network connection works, then install it again.

If that doesn't help, send me the following file:

/Library/Preferences/SystemConfiguration/Preferences.plist

Then I should be able to resolve this problem.  
(Version 1.0.4)