I was about to post my question here when I looked at the SMF Recent Posts php file and compared it to the SMF Recent Events php file. Basically I have a module class assigned to both and it looks fine in IE and Firefox for the Recent Posts, but the Recent Events module table header background image was being cut off in Firefox and the text wasn't centered.
I resolved the problem by enclosing the SMF Recent Events script in table tags like the Recent Posts script, i.e., echo '<table border="0" class="', $moduleclass_sfx ,'">';
echo '</table>';
Thought I'd post anyway since nothing came up in the search I did....