Friend electric define ".item-list ul" display to "block" wich cause problem under IE 6 (the trash icon and the bookmark name are not on the same line and this break the column ).
On way to avoid this would be to set

.block-bookmarks .item-list ul li a, .block-bookmarks li.expanded a, .block-bookmarks  li.collapsed a, .block-bookmarks  li.leaf a {
  display: inline ;
}

but i'm not sure this is the best way to do.