Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Hi, That was really helpful and I've identified the cause of the problem. It's Firefox Colour Theme https://color.firefox.com/ where one can choose one's own colour scheme. If I switch that off the problem is gone.

Any ideas how I can choose the colours of Firefox without using Firefox Colour Theme? Or will they fix the bug? It used to work fine.

Do you see the text if you select a bookmark in case text and background color are the same ?

• https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/theme#colors

Brilliant! Thank you so much. I had got some of the text set to white. Stupid of me not to have thought of that but thanks a million.