First things first, these are great time-savers & I use the feature a LOT.
Second, it struck me that while LMB = Go Back and RMB = Go Up are great using middle-click to go to the root directory of a drive would be a useful addition.
I´m quite sure you can do that already 
If you go to -> settings -> file types -> all file & folders -> edit -> middle double click, you can
use GO Root. That should do it already.
[quote="abr"]If you go to -> settings -> file types -> all file & folders -> edit -> middle double click, you can
use GO Root. That should do it already.[/quote]
That would make it so that middle-clicking on any file or folder would take you to the root. It would not affect the slide-out navigation buttons in any way.
Re the main request, I guess MMB on the buttons doesn't do anything right now so there wouldn't be any harm in making it go to the root.
Ok, true. This rather was meant as a workaround to quickly access the root.