That sounds more like something added by an extension.

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do not click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Thanks for replying. I tried to restart in Safe Mode, but id did not change anything (and I always used the default theme.)

Actually, after having been caught with Tab Groups, I came back to the usual tabs, including the arrows left and right to circulate through them and the small menu on the right "List all tabs" that I like to use by deleting the "sessionstore.js" file in my profile...

The only remaining annoyance now is that little 3x3 squares icon "show/hide the new tab page" which comes on the right of every new tab page: clicking "show" brings in the page a number of miniature pages which I had formerly visited but do not need anymore.

Clicking on any of these brings it in the same tab page, but closing that tab and calling for a new tab brings the same group of page miniatures again.

I'd like to get rid of this... Any solution?

I'