I've been wishing for this functionality in Firefox, but not enough to go looking for it - until today. Found a couple add-ons that help when organizing the bookmarks library:
Go Parent Folder - Adds a "Go Parent Folder" option to the context menu in the bookmarks library. Opens the parent folder of the current bookmark in the folder tree (left pane).
Show Parent Folder - Makes a "Parent Folder" column available in the bookmarks library search results (right pane).