uses
 Registry;
{....}
procedure TForm1.Button1Click(Sender: TObject);
var
 Reg: TRegistry;
 KeyName: string;
 ValueStr: string;
begin
 Reg := TRegistry.Create;
 try
  Reg.RootKey := HKEY_CLASSES_ROOT;
  KeyName := 'htmlfile\shell\open\command';
  if Reg.OpenKey(KeyName, False) then
  begin
  ValueStr := Reg.ReadString('');
  Reg.CloseKey;
  Label1.Caption := ValueStr;
  end
  else
  ShowMessage('No Default Webbrowser !');
 finally
  Reg.Free;
 end;
end;