Public Class wbForm
    Public Sub NewTab(ByVal url As String)
        Dim NewBrowser As New UserControl1
        Dim NewTab As New TabPage
        NewTab.Controls.Add(NewBrowser)
        NewBrowser.Dock = DockStyle.Fill
        TabControl1.TabPages.Add(NewTab)
 
        If url = "" Then url = "http://google.de"
        NewBrowser.wb.Navigate(url)
        MsgBox(url)
    End Sub
 
    Public Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        NewTab("")
    End Sub
End Class

Public Class UserControl1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        wbForm.NewTab("http://yahoo.de")
    End Sub
End Class