If you mean from the Bookmarks menu on the main menu bar then that isn't possible on Mac.
On other platforms (Windows, Linux) you should be able to do this via an extension or code in userChrome.css, but on Mac the menu bar is controlled by the Mac OS and can't be modified this way.

OK, so is there a way to do anything about this "Unsorted Bookmarks" folder on a Mac or is it just something to live with .... ?

Best would be to move all bookmarks in the Unsorted Bookmarks folder to a folder in the Bookmark Menu folder or the Bookmarks Toolbar. That would only leave you with the menu entry.

Clicking the star in the location bar will bookmark the page in the "Unsorted Bookmarks" folder and the star turns yellow (blue on Mac) to show that.
Click the highlighted star a second time to open the "Edit This Bookmark" pop-up and move the bookmark to another folder or edit the name.

Save these lines in your userChrome.css. Alternately you can save them as a userStyle in Stylish instead of userChrome.css.