Launching a web browser using the PYUNO bindings

Hi,

I'm trying to launch the default web browser to load an html file with
the preview of the web wizard results.

Im trying to get a dispatcher using the following code:

  xDispatch = xFrame.queryDispatch(oURL, "_top", ALL)

Being oURL:

(com.sun.star.util.URL){ Complete = (string)".uno:OpenHyperlink", Main =
(string)"", Protocol = (string)"", User = (string)"", Password =
(string)"", Server = (string)"", Port = (short)0x0, Path = (string)"",
Name = (string)"", Arguments = (string)"", Mark = (string)"" }

The xFrame instance is acquired as follows:

  xDesktop = xMSF.createInstance( "com.sun.star.frame.Desktop")
  xFrame = xDesktop.findFrame("_blank", 0)

I've got several browsers installed in my environment (Ubuntu Quantal)
and it works fine using the java version of the web wizard.

Any idea why I'm getting always NULL as result of the queryDispatch call ?

Thanks,