Hi spiper42!

These forums might help: _________________________ https://support.mozilla.org/en-US/questions/1266124 https://support.mozilla.org/en-US/questions/925894 _________________________ Did this answer your question?

Make sure you are not blocking content.

Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop

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• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}acking-protection-firefox-desktop

Hi all, i have just had to reinstall windows 10, SSD failure warnings. i have reinstalled firefox. typing this the thick black rectangle has just appeared and then disappeared! all within the rectangle is reduced in size, it appears and disappears whilst typing this. this rectangle appeared before i had managed to login to my account to sync data.

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

You can also try to disable WebRender and leave hardware acceleration enabled.

You can look at these prefs on the about:config page page to enable or disable WebRender.

• gfx.webrender.enabled = false|true
• gfx.webrender.force-disabled = true|false

You can open the about:config page via the location/address bar. You can click the button to "Accept the Risk and Continue".

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

thank you cor-el. tried many of the suggestions. altered the graphics acceleration in preferences and that seemed to work. I have altered the about:config as you suggested, changed both to the opposite value and reset the accleration setting back to the original. the above has got rid of the large thick walled black rectangle

seemed to work for a while, then I had to go back into about:config and reverse one of the options. will keep you all updated if it reappears.