That sounds like a font issue.

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Thank you!

The picture and the letter they will distorted them in 15-20 minutes of time! -First look on the web page it look fine it! https://screenshots.firefox.com/SU0d8n9ZURGTE9Tb/support.mozilla.org -Am I do it right? I did press the save button on the screenshot! S.

Note: I can not copy the image of the distorted web page because when I try to screenshot the web page the image become a clear image!S.

You can try to disable hardware acceleration in Firefox.

• Options/Preferences -> General: Performance
  remove checkmark: [ ] "Use recommended performance settings"
  remove checkmark: [ ] "Use hardware acceleration when available"
• https://support.mozilla.org/en-US/kb/performance-settings

Close and restart Firefox after modifying the setting for changes to take effect.

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

You can check if there is an update for your graphics display driver and check for hardware acceleration related issues.

• https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration

Make sure you allow pages to choose their own fonts.

• Options/Preferences -> General: Fonts & Colors -> Advanced
  [X] "Allow pages to choose their own fonts, instead of my selections above"

• https://support.mozilla.org/en-US/kb/websites-look-wrong-or-appear-differently

Thank you! S.