how to prevent focus event in IE when mousedown happens

You can use "unselectable" attribute for prevent losing focus in IE and mousedown handler for other.

<input type="text" id="name">

<div onmousedown="return false" unselectable="on" id="suggest">
  <div unselectable="on">mark</div>
  <div unselectable="on">sam</div>
  <div unselectable="on">john</div>
</div>