Mozilla’s development team introduced several new dynamic bookmark folders in Firefox 3 including the recently bookmarked, unsorted bookmarks and recent tags folders.
All but the unsorted bookmarks folder are displayed in the default Firefox bookmarks menu. The unsorted bookmarks folder on the other hand is only visible in the Firefox bookmarks manager and not in the menu.
Update: In recent versions of Firefox, unsorted bookmarks is displayed along with all other bookmark folders when you click on the bookmarks menu button. The guide can still be useful if you want to move the unsorted bookmarks folder to another location.
It is unclear why that decision has been made by the developers as it is quite uncomfortable to access the unsorted bookmarks this way.
Remember that new bookmarks that get added by clicking on the star in the Firefox address bar appear in the unsorted bookmarks folder unless you select another destination for them manually.
There are actually two solutions to improve the visibility of the unsorted bookmarks folder.
The first option is to go into the Firefox bookmarks manager with a tap on Ctrl-Shift-b and drag and dropg the unsorted bookmarks folder to a different location. This can be either one of the toolbars or a location that is visible in the Firefox bookmarks menu.
The second option is to add a new bookmark in the location the unsorted bookmarks folder should appear and add the following line as the location:
place:folder=UNFILED_BOOKMARKS
The name of the bookmark folder can be freely selected. It may be required to restart Firefox before the folder is accessible in the web browser though so if it does not appear right away restart Firefox to make it appear.
Dragging and dropping the unsorted bookmarks folder is probably the best way of moving the unsorted bookmarks folder to another location as it is easily done and visibly right away.