What exactly happens? Do you see the page below?

If you see it but it looks like different, you could send a screenshot.

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

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

If you want to revert changes made to the search bar then you can toggle this pref to false with a middle-click on the about:config page to restore the previously used standalone window to manage the search engines.

• browser.search.showOneOffButtons = false

Close and restart Firefox to make the change effective.

Banban: Yes, that is what I see but I can't modify anything on that page or select anything from the menu on the left.

cor-el: Everything worked in FF Safe Mode. So in Normal Mode I disabled Add-ons one by one. Turned out to be the Aeon Clouds 7.5 theme. This is odd because on my previous computer with the same OS and FF vers. I had no problems with Aeon Clouds 7.5 .

Thanks for your help!