Tested in Firefox developer edition
Hi, I used this two files (window_control_placeholder_support.css + hide_tabs_toolbar.css) for tree-tabs but seems like they will need an update. The window controls only shows when press Alt and the menubar shows behind the urlbar.
Sure, it’s possible. But never really an intended feature of hide tabs toolbar, it was just necessary to do it because of how the old style worked. But if you want to have menubar work like that then I think you can use overlay_menubar.css with the v2 hide tabs toolbar.