You’re able to edit it. It isn’t straight forward as it could be in letting you know
how to do this, but you can edit it easily. For example, when you’re at a website/page you want to add to frequently visited: click the location bar to show the website’s icon, then drag it to frequently visited.
You’re able to drag icons out of frequently visited to delete them, and if you’re editing your frequently visited list while in a new window or tab (not through clicking the location bar to show it), try dragging them off the main center area of that window/tab to delete.