Add (optional) scroll bars to the UI XUL in a few places
There are several places in the UI where our UI dialogs have become large enough that users on small screen devices (like 16:9 netbooks, ugh) can't see them properly. This problem is most severe with about.xul and observatory-preferences.xul, though observatory-popup.xul and preferences.xul might be affected too.
Our XUL should be smarter about not sizing these windows taller than the screen, and adding scrollbars if but only if they're necessary.