This sounds like it could be a graphics issue with Firefox.

First, check if the issue occurs while running in Firefox Safe Mode. Safe Mode is a troubleshooting mode that temporarily disables add-ons, changes some settings and (most importantly in this case) disables hardware acceleration.

If the issue doesn't happen in Safe Mode, your issue is likely with hardware acceleration. Since it sounds like it may be a randomly occurring issue, you may have to run in Safe Mode for an extended period of time to ensure that the issue is gone in Safe Mode.

If it's a hardware acceleration issue, you should ensure that your graphics drivers for your computer are up-to-date, since outdated versions of these drivers can cause these types of issues. You will need to restart your computer after updating to see any changes.

If that does not help, you may need to disable hardware acceleration in Firefox. You will need to restart Firefox to see any changes.

Hope this helps.

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 causing the problem.

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

I never have change theme at firefox. NEVER.

You mean that at picture? My firefox language is Greek. I have it at default state.

Maybe i try some times to change it to "hardware accelerate mode" and change to number 1 or 2 but return it to defalt state and now i have it to default state.

Anything new???

Still we don't find the solution to this problem.

I try to disable hardware acceleration but it wasn't that.