There is a visualization bug under IE6 when you are trying to use ajax tabs. See attached image.

The solution is use <p> tag instead of <em>:

Line 487: 
$span.data('label.tabs', $span.html()).html('<em>' + o.spinner + '</em>');

replace to

Line 487: 
$span.data('label.tabs', $span.html()).html('<p>' + o.spinner + '</p>');

Also you should fix a .css file, replace .ui-tabs-loading em to .ui-tabs-loading p and add padding:

.ui-tabs-loading p {
    padding-left: 20px;
    background: url(loading.gif) no-repeat 0px 50%;
}