This sounds like screen tearing, which isn't directly related to Firefox. You may want to checkout this website for instructions on how to enable vsync on your Linux distro for whatever graphics card you have.

Other than that, the only thing I can think of that may help is to disable hardware acceleration in Firefox.

Hope this helps.

Hello,

shlomo_bachar........

Try disabling graphics hardware acceleration. Since this feature was added to Firefox, it has gradually improved, but there still are a few glitches.

You will need to restart Firefox for this to take effect so save all work first (e.g., mail you are composing, online documents you're editing, etc.).

Then perform these steps:

   Click the menu button New Fx Menu and select Options on Windows or Preferences on Mac or Linux.
   Select the Advanced panel and then the General tab.
   Uncheck Use hardware acceleration when available.
   Restart Firefox and see if the problems persist. 

Did this fix your problems? Please report back to us!

If the problem is resolved, you should check for updates for your graphics driver by following the steps mentioned in these Knowledge base articles:

   Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems 

   Upgrade your graphics drivers to use hardware acceleration and WebGL 

Thank you.