hello UnderPar, go to the new firefox menu > customize and enable the title bar on the bottom left of that window...

Thank you so much, Phillip! It was well-hidden.

As a site owner and just generally, it's a loss not to have the titles as a default. Will this be changed back at any point?

Page titles appear on each Tab, although longer page titles will be truncated to fit the size of the tab; but on mouse hover the full page title will appear in a tooltip - so there's no "loss" for the user, who just needs to be aware of the features in Firefox.

Just living without that bar for a week proves that hovering isn't a solution. Obviously the easy solution is given by the correspondents that explained about the triple-line menu and its options option, and the toggle at the bottom left corner which immediately fixes this annoying new default option. Thanks to all. (I had been lost in about:config when I found your solution.)