Oh, whoops. I should have said "page". How do I open a page in a pop up style window. Not multiple tabs in a pop up window. Basically what I want is a window that's as compact as possible. Without editing the settings of my main window.
If you open a new window and hide all the toolbars (View > Toolbars or Firefox > Options) for maximum browser space then you can bring up a location bar replacement with the Ctrl+L shortcut. Ctrl+T should open a new tab in such a window or a middle-click or a double-click on the tab bar if the tab bar is already visible.