sub open_default_browser {
  my $url = shift;
  my $platform = $^O;
  my $cmd;
  if ($platform eq 'MSWin32') { $cmd = "start $url";             } # Win95..Win7
  if (defined $cmd) {
    system($cmd);
  } else {
    die "Can't locate default browser";
  }
}

open_default_browser("http://www.gmail.com/");