You need a button to open the Bookmarks sidebar. You can either use the Classic Theme Restorer extension to get such a button or use the "Show sidebars" button that you can find in the Customize palette.

Make sure to use the correct button if you have the CTR extension.

Thank you cor-el for your kind and prompt reply.

As an alternative, I have already started using the Sidebar button in the Toolbar, but frankly it's not as convenient as that sweet drop-down menu i referred to in my question, and it shows only Bookmarks, not Favorites. For the latter, I have to go to the Toolbar menu, and click on Favorites, which then displays as a drop-down menu. Not bad, but not as convenient.

The CTR extension should make such a button available in the Customize palette, so you may want to give that another check. There are two such star buttons in the palette and one gives a drop-down marker when placed on the toolbar and you need the other that opens the bookmarks sidebar and drag that to the Navigation Toolbar.

I have the Show Sidebars button at the left end of the the Toolbar. It displays either Bookmarks or History, and can be accessed either by clicking on it or by keyboard command, making it pretty convenient.

I now also have the double-star button for Bookmarks and Favorites at the right end of the Toolbar (the right end being the only place on the Toolbar where it works properly). Clicking on the Favorites side of the button produces a convenient pull-down menu, but clicking on the Bookmarks side opens the Bookmarks window, not as convenient.

I'll use the Show Sidebars button for Bookmarks, and the Favorites (starred) button for Favorites. Not as cool an arrangement as under 3.0, but I'll live with it. Seems the powers-that-be always give with one hand and take with the other.

Thanks for your help, cor-el -- much appreciated.