It sort of does. I can't open settings in a new window without opening settings in a new tab first and then moving the tab to a new window. Or, create a new window and paste about:preferences into the url bar. Maybe there's some userChrome.css to do it.
I can create userChrome.css, which is discouraged, in order to hide the redundant tab bar with the single tab in it. Yes, it sort of works, it's kludgy and has issues.
Just remove them completely and let you window manager manage your windows.
(And yes, Firefox still supports browsing without tabs, so we got what we need right there ;)