Are these bookmarks you added that you no longer need?

If you right-click/Ctrl+click a Firefox bookmark either on the Bookmarks Toolbar or on the Bookmarks menu, you should get a short context menu with a Delete command.

To operate on multiple bookmarks at once, you can use the Library dialog. Either:

• Command+Shift+b
• "Show All Bookmarks" from the Bookmarks menu

Is that what you meant, or is Firefox making suggestions from history or another source that you want to remove?

See also:

• https://support.mozilla.org/kb/how-do-i-delete-bookmark