The star with the underline (tooltip: "show your bookmarks") is the Bookmarks Menu button that shows all bookmarks in a drop-down list similar to the Bookmarks menu.

• you can tap the Alt key or press the F10 key to show the hidden Menu Bar temporarily

The Bookmarks Menu button was previously and second part of the bookmarks star, but is a separate button now that the star has moved to the page actions container (three dot menu in the location bar). Note that in Firefox 60+ all buttons in the location bar will move to the left end of the location bar.

• https://support.mozilla.org/en-US/kb/bookmarks-firefox

Why change what was easy to understand and familiar?

Hi, things move along and never stands still in tech. Turn on the Firefox Menu Bar, I still use it. Says Bookmarks and I have not stuck the others up with the Customize Settings. All are shown in the URL provided by cor-el