Well, in tests here, I get a slight space in both browsers using just the word 'Hi' in a single celled table with your hr below it but, the IE gap is larger. In any event, giving either the hr a negative top margin or the table a negative bottom margin will close the gap. If this messes up the positioning in FF you can use the !important hack:
HTML Code:
<table style="margin-bottom:0!important;margin-bottom:-8px;">
If you are wanting to avoid problems with Opera and possibly other browsers, including IE Mac, look into more specific hacks at quirksmode.org.
Bookmarks