Not that Firefox wasn't the most customizable browser already, but the upcoming edition will allow you to add and remove elements from all installed toolbars – paring your experience down to a single row, if desired.
As someone who currently uses three rows of toolbars, plus the area taken up by in-browser tabs, screen real estate is always an issue. Moving to larger monitors & screen resolutions does help, but it remains a constant balance between adding functionality -vs- viewable area. Knowing that I'm overly reliant on my 'bookmarks toolbar' – which I jam as many essential links into as possible – the idea of consolidating the rest of my browser experience into a single toolbar is very appealing.
For many of us, the browser is now our primary computer interface. Anyone else care to share a tip on making that experience more productive?