Bug: User preferences dialog does not scroll if the window is too short

If the window is not tall enough to show the entire preferences screen, it does not scroll.

It's not possible to see the bottom of the screen, and the Save button may not be accessible.

Start by reproducing the issue with a window too short to show the full user preferences dialog, then locate the JavaScript and UI markup responsible for that screen. The work is done when the dialog can scroll far enough to reveal every preference and the Save button at short window heights.

Written by the indexing model from the issue text.