With the tabs on top, bookmarks toolbar does not belong below the tabs. I believe there's an add-on to move the bookmarks toolbar above the tabs, but I have moved them next to the firefox menu bar, which makes good use of space. However, view->toolbars->bookmarks toolbar: hide, hides only the now empty bookmarks toolbar (container), not the items, since dragging by view->toolbars->customise does not move the toolbar but moves the items out of it, so the view setting no longer affects them. In full-screen, I can't get them at all.