The sidebar is based on an early work :target Tabs.
What Should Happen?
When you click on ↘ next to the link on the sidebar content should appear underneath the link.
Mozilla PR 1.3 (Gecko/20030310) works fine with fixed positioning. This was a problem in Mozilla 1.3b where it did not work when the sidebar is fixed positioned (
Veiw > Use Style > Fixed Positioning) .