Downloaded nightly build 131055, and launching Webkit throw an alert Window : OS X 10.6 not supported. Nightly builds of Webkit are not currently supported on OS X 10.6 at this time. Downloaded last 131199 build, and same problem. Does OS X 10.7 is a prerequisite for webkit now ?
That is correct. Nightly builds are intended for testing with the most recent Safari release, and Safari 6.0.1 is not available for Snow Leopard.