Thanks to Matt, the human Internet search engine, we have an answer for why the doctype defn in yesterday's "excercise" blew things up:

We notice that the doctype had "The public identifier "-//W3C//DTD HTML 4.01 Transitional//EN", with a system identifier." This puts Mozilla into "strict" mode, which causes bugs to happen with stuff like that described here:

If your bug is with the layout of a particular web page, and the problem is caused by either:

The page using proprietary HTML, such as the LAYER tag
The page using proprietary DOM extensions, such as document.all
The page being rendered in quirks mode (as described above)

Sure enough, the second one, in bold, is what the page was using, so document.all was out the window and, with it, the menu.