It needs jShell library. You must call the sub immediately after srvr.Start and before StartMessageLoop.
B4X:
Private Sub WindowsStartPage
Select Case GetSystemProperty("os.name", "").ToLowerCase.Contains("win")
Case True
Dim sh As Shell
Dim shresult As ShellSyncResult
sh.Initialize("sh", "cmd", Array As String("/c", "start", "http://localhost:51042"))
shresult = sh.RunSynchronous(1500)
Log(shresult.StdOut)
Case False
End Select
End Sub