You don't do sub-folders, i.e. folders within folders!

Alan Perx 6 years ago in FVD Speed Dial / Firefox 0
a couple of other speed dial add-ons do it without any problems.

Also, the way you layout a choice of only FIVE folders along the top "menu" bar is mental.  The folders are supposed to be icons we click on.  The whole point of the Speed Dial metaphore is to click on icons everywhere! no more menu bars or drop down menus, OK?