The Firefox 85 version is scheduled to include an option that would allow users to remove the "Other Bookmarks" button, but this is not available yet for Firefox 84.x users.

On the Bookmarks Toolbar, the Live Bookmarks folder for a website is marked with a standard Firefox folder icon marked with an orange feed icon. To delete this folder, right-click it and select ...

Mozilla's macOS Firefox browser stores cached files on your Startup Disk and can take up space. This is how to reset Firefox to get back some of that consumed storage.