{....}
 private
  procedure SearchAndHighlightText(aText: string);
{....}
procedure TForm1.SearchAndHighlightText(aText: string);
var
 i: Integer;
begin
 for i := 0 to WebBrowser1.OleObject.Document.All.Length - 1 do
 begin
  if Pos(aText, WebBrowser1.OleObject.Document.All.Item(i).InnerText) <> 0 then
  begin
  WebBrowser1.OleObject.Document.All.Item(i).Style.Color := '#FFFF00';
  WebBrowser1.OleObject.Document.All.Item(i).ScrollIntoView(True);
  end;
 end;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
 SearchAndHighlightText('some text...');
end;