Hi! A similar behavior has been identified in the past as an effect of the Hardware acceleration. Check if that option is selected and if so, just uncheck it. Learn more about it in the following link: [https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems?s=hardware+aceleration&r=1&as=s#w_turn-off-hardware-acceleration Turn off Hardware Acceleration] Let me know if it helps.