There are two kinds of windows in question here.

It's long been possible to pop up a new window without buttons, the address bar, status bar, etc. The HabitableZone message window and the popup windows on mgs.com are examples. It's just a matter of specifying window features in the script function that pops up a window.

The new thing Mozilla provides is a way to control the visibility of controls on an existing window. You'd go to the Nexus, and it would make the buttons et al disappear. It'd probably be a good idea if all that stuff reappeared when you leave the site.

From the feedback you and Tony provided, it sounds like I guessed right about user psychology. I should make disappearing controls a configurable option and not do it unilaterally. I think it'd be a useful feature, not only to avoid confusion in the operation of the interface, but to conserve screen real estate as well. People with displays smaller than 1024x768 seem to really struggle with the interface.

Thanks for the feedback.