Please delete/ignore this page since it is already covered in /CompareButtonFailsToDiff
I tried with Firefox and Internet Explorer, since in the DoHistory() function the <form action uses single quote it cannot compare versions of pages with single quote in their name (as this page). To test this: select "View other revisions" of this page and press the compare button, you will be going to a different page: /DoHistory instead of DoHistory's_Form.
I've changed this replacing the single quotes with double quotes:
if ($UseDiff) { print <<EOF ; <form action="$ScriptName" METHOD="GET"> <input type="hidden" name="action" value="browse"/> <input type="hidden" name="diff" value="1"/> <input type="hidden" name="id" value="$id"/> <table border="0" width="100%"><tr> EOF }