or download this
_template/tt2/diff_button.html__
<!-- BEGIN diff_button.html -->
<a href="[% script_name %]?action=diff&page_name=[% page_uri %]&revisi
+on_id=[% revision_id %]" accesskey="r" title="Differences">[% INCLUDE
+ diff_button_icon.html %]</a>
<!-- END diff_button.html -->