Rated 5 out of 5 stars

This addon in combination with Vertical Bookmarks Toolbar made it possible to get the bookmarks into a vertical bar.

Unfortunately Vertical Bookmarks Toolbar is broken on FF15 and the author doesn't want to maintain it any longer.

Maybe someone else would like to maintain it?

UPDATE: Thank you Gomita. I really like it the way it works now. You're the best! :-)

This review is for a previous version of the add-on ( 

Try Vertical Toolbar 0.3 which displays Bookmarks Toolbar Items vertically.