Using Selenium Server interactive on OS X
cmd=getNewBrowserSession&1=*safari&2=
http://localhost
The command will never return because it will ignore our configured proxy server for localhost. Same applies to 127.0.0.1. Setting a real host name (configuring one in /etc/hosts if necessary) will fix the problem.
In fact, this is true even if you just configure the proxy using the Network control panel using the GUI. There appears to be no way to disable this "feature."