Firefox has three main buckets of bookmarks: Bookmarks Menu, Bookmarks Toolbar, Other Bookmarks.

If you want the folders on the Bookmarks Menu instead of on the Bookmarks Toolbar, you could move them over. Easiest to do that in the Library window. See: Use bookmark folders to organize your bookmarks.

But if you want to keep the folders on the Bookmarks Toolbar and only work with the Bookmarks Toolbar from the sidebar or drop-down menu, then... maybe:

(1) You could hide the Bookmarks Toolbar

Bookmarks Toolbar - Display your favorite websites at the top of the Firefox window

(2) If you want to use the Bookmarks Toolbar for other icons, you could remove the "Bookmarks Toolbar Items" container from the toolbar. To do that, open the Customize tab, then drag it from the bar into the box of un-used controls and buttons.

Customize Firefox controls, buttons and toolbars

Does either of those approaches meet your needs?

You created another thread where you want the opposite:

• /questions/1330357 Remove folders from the bookmark menu

I want to remove folders from the bookmark menu and keep them in the bookmark toolbar. I need the space in the menu for websites not folders. Thank you

Can you clarify what you want to achieve ? Where would you want to free up space ?

Can you attach a screenshot?

• https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem
• use a compressed image type like PNG or JPG to save the screenshot