To tell you the truth, I have not used the Unsorted Bookmarks feature in Firefox 3 that much at all.  Why?  Well, it is a ‘bit of a pain to get to.  You have to open your bookmark manager, open up all bookmarks in the tree then go down to unsorted bookmarks.  Want an easier way to access your unsorted bookmarks?

Right-click on your bookmarks toolbar, and select “New Bookmark”.

The name can be anything.  To keep things simple, for now we will just call it “Unsorted Bookmarks”.  You might want to shorten that to “ubooks”, “ub” or something like that if you want to save bookmark toolbar space.  Now for the location, type this smart bookmark string in:

place:folder=UNFILED_BOOKMARKS

Now hit the “Add” button, and you should see a new folder popup on your bookmarks toolbar named “Unsorted Bookmarks”.  Click on it as you would with any other bookmark folder, and you can see all of your bookmarks that have not yet been categorized into the rest of your bookmark folders.

UPDATE: For Firefox 3.5 (or for any version where this is not working) try to restart Firefox, then see if it works.  So add this bookmark, restart Firefox, then re-launch Firefox and it should work.