Change the default Bookmarks Folder In Firefox

The Bookmarks Toolbar option is inbuilt into 68.02.2 (64 bit).

If it's not already visible on your system you need to perform the following steps (which don't involve add-ons).

Press F10 or Alt to get the menu bar [File Edit View etc] at the top of the FireFox menu bar.

Then select view→Toolbars→Bookmarks Toolbar and ensure that there is a ✓ next to Bookmarks Toolbar.

You can the drag and drop pages as required either directly on to the Bookmarks Toolbar or down in to the Bookmarks option in the sidebar (you may need to ensure that view→Sidebar→Bookmarks is also showing a ✔

Since there is no possible way to change the default bookmarks folder without add-ons, I found myself obliged to use one (Default Bookmark Folder).
By using this add-on, it is possible to change the default bookmarks folder to any other folder (Bookmarks Toolbar in my case).

It even has a quick bookmarking feature.

This feature will add a quick bookmark icon in the address bar, to (un)bookmark a page with only one click. The icon is a round star icon in the address bar. If the current page is bookmarked, the icon color will change to the selected color (red by default). Here is a screenshot to serve as examples: when the current page is not bookmarked and when it is.