use target=_blank

jdav_web/templates/admin/finance/statementconfirmed/change_form_object_tools.html

@@ -9,7 +9,7 @@
 </li>
 <li>
     {% url opts|admin_urlname:'summary' original.pk|admin_urlquote as invite_url %}
-    <a class="historylink" href="{% add_preserved_filters invite_url %}">{% trans 'Download summary' %}</a>
+    <a class="historylink" target="_blank" href="{% add_preserved_filters invite_url %}">{% trans 'Download summary' %}</a>
 </li>
 {{block.super}}