This cannot be done.
You can move the bookmarks from inside, but you cannot delete the folders because they are programmed into Firefox.
Sorry.

Bah, thanks anyways

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You can't remove any of the three main root folders.
You can possibly hide them with code in userChrome.css.

Add code to the userChrome.css file below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

The customization files userChrome.css (user interface) and userContent.css (websites) are located in the chrome folder in the Firefox profile folder.

• http://kb.mozillazine.org/Editing_configuration

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

#BMB_bookmarksToolbar,
#BMB_bookmarksToolbar+menuseparator,

#bookmarksToolbarFolderMenu,
#bookmarksToolbarFolderMenu+menuseparator,

#appmenu_bookmarksToolbar,
#appmenu_bookmarksToolbar+menuseparator,

#BMB_bookmarksPopup menuseparator[builder="end"],
#BMB_unsortedBookmarks,

#bookmarksMenuPopup menuseparator[builder="end"],
#menu_unsortedBookmarks,

#appmenu_bookmarksPopup menuseparator[builder="end"],
#appmenu_unsortedBookmarks {
 display: none !important;
}