>>It will only catch people who have configured their proxy very poorly.
To add to this, in Firefox if you use this: http://i.imgur.com/ajT98xC.png , Flash does not obey it. I kinda think Mozilla should put some kind of warning-text on this dialog window to warn uses that it doesn't apply to flash, silverlight or any plugins. This surprised me at first but it makes sense if you think about it. You really have to do a system-wide VPN type thing. Something like this: https://github.com/apenwarr/sshuttle will actually tunnel everything on your PC.