Customizing Firefox for Use in Windows 8.1
To organize your bookmarks into folders or place bookmarks on the Bookmark bar, click the down arrow to the right of the Folder box.
Firefox lets you choose the bookmark folder that should contain your new bookmark or create a new folder to hold the bookmark.
If you create a new folder, you can leave it in the Unsorted Bookmarks folder, but if you want to make it more readily accessible from the Bookmarks menu, click and drag the new folder in the Edit This Bookmark dialog box so that the folder appears under the Bookmarks Menu folder.
If you want to put the new folder on the Bookmarks toolbar, to the right of the Latest Headlines button, click and drag it to the Bookmarks Toolbar folder.
The Bookmarks toolbar is convenient, but it takes up precious space on the screen. Many people prefer to work with the Bookmarks icon, on the far right.
After the folder has been created (and, optionally, located on the Bookmarks menu or the Bookmarks toolbar), you can place any bookmark in the folder by double-clicking the bookmark star.