Thanks so much, Stephen. I must admit that I rebooted into Windows with much doubt. But lo and behold when I cleared eventhing (cache, cookies, etc.), the menus worked properly! But if you have another minute or two, could you explain how cache could have caused the problem? I always try to learn as much as I can from problem solutions. I even noticed that one of my settings was to "automatically" look for latest page version. Here's something that might help in diagnosing the problem. I neglected to describe what the problem had been for me, so here it is:
(1) In the main vertical menu, the right side border did not appear.
(2) Even without the mouse over any part of the main menu, when one of the main menu items has a popout, I have an arrow at the right hand side of the main menu item name. Those arrows were missing.
(3) When moving the mouse down the main menu, the secondary menus poped out, but when you moved the mouse onto it to select an item, the whole poped out column immediately disappeared.
Again, where's the connection with cached pages? I'd really love to learn the explanation. Thanks so much.