·Verizon Online DSL
My first thought was, why shouldn't it happen?
But looking now, I see it is kind of difficult to do it - in FF.
(Sucks IMO, because I like the ability to create dups. SeaMonkey still can, easily.)
Though it can be done.
I'm just now sure how I did it?
Actually I ended up with the same bookmark three times. Twice in 'Recently Bookmarked' (is that something that is "real" ?) & once in 'Unsorted Bookmarks'. Depending on how you bookmark, like if you use the 'Star' instead of the context-menu, a bookmark may end up going one place & not another. Never really understood that, much less the reason for that happening?