Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -&gt; Add

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

switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance

do NOT click the "Refresh Firefox" button on the Safe Mode start window

https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems