procedure TForm4.WebButton2Click(Sender: TObject);

procedure DialogProc(AValue: TModalResult);
  var
    s: string;
  begin
    if AValue = mrYes then
    begin
    WebButton2.Caption:='mbYes';
    end;

    if AValue = mrNo then
    begin
    WebButton2.Caption:='mbNo';
    end;


  end;

begin
  MessageDlg(WebEdit1.Text, mtConfirmation, [mbYes, mbNo], @DialogProc);

end;