Go to about:config and in the search box type browser.tabs.hoverPreview.enabled. That will then appear below with the word true next to it. Double-click true and it will change to false.

This is what it looks like before I make any changes. It seems to be just like you suggest. But the text for each tab is still there 🤷‍♂️

Sorry I slightly mis-understood what you were asking.

Firefox has always popped up a small notice below hovered-on tabs as if a lot are open they become too small to see the labels on them.

Recently they have made these pop-ups more intrusive and I thought you were wanting to disable those. As far as I am aware you can't get rid of the old discrete one.

See the picture below to see what the varies combinations of settings can do. Not much help to you but hopefully it may be of use to other people as the a lot of us don't like the new ones.

Thanks for your fast replies!