"Bookmark this Page" and "Manage Bookmarks" can't be dragged, so that one should not be dragged also. It more or less happens because that menu-item has an id, so removing that id would disable the dragging. Although it is rather odd that this depends on the existence of an id. Maybe it would be better to check for a nodrag attribute or something.
Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8b4) Gecko/20050816 Firefox/1.0+ ID:2005081610 Confirmed on branch
See: http://bonsai.mozilla.org/cvsblame.cgi?file=mozilla/browser/components/bookmarks/content/bookmarksMenu.js&rev=1.48&root=/cvsroot#670 which I think is part of the code that is involved here.
Well, this is fixed somehow, no idea how or when it was fixed.