Styling <hr /> tags across different browsers doesn't work. Instead use <div> tag with a class applied.
<div class="hr"></div>
to produce:
The css required is:
.hr {
padding: 0;
margin: 0;
padding: 1px;
background: transparent url(images/black_dotted_hr_bg.gif) repeat-x bottom;
line-height: 1px;
}