In Firefox, go to Bookmarks/Bookmarks Manager

Go to the Folder in Bookmarks from where you want to copy Bookmarks

If you select one bookmark it will become coloured.

You could copy one Bookmark to Fast Dial or with CTRL pressed down, add further bookmarks to your first selection.

When you have selected all the files you wish to copy to Fast Dial then right click copy.

Go the Fast Dial Folder of your choice in Bookmarks

(Either the Root or any Folder)

Open the Folder and right click and paste onto the Folder Page (right of screen)

This will copy all of your selected bookmarks to the Fast Dial Folder of your choice.

When you open the folder in Fast Dial the bookmarks will appear.

Many thanks