Does Safe Mode in Firefox help? How to start Safe Mode: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode#w_how-to-start-firefox-in-safe-mode.

Safe Mode will nix hardware acceleration and any extensions and themes that may be causing the issue.

check this:

• see if there are updates for your graphics drive drivers

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

• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)

https://forums.adobe.com/message/4468493#TemporaryWorkaround

• disable hardware acceleration in the Flash plugin

https://forums.adobe.com/thread/891337 See also:

• http://kb.mozillazine.org/Flash#Troubleshooting

Ah, yes, disabling hardware acceleration seems to have solved it. I should have thought of that...

Great! You could try updating drivers as Fred suggested to see if that helps hardware acceleration, but I think that's it for now.

Thanks for reporting back and please mark an answer as a solution so the Question can be Solved; use the button right of the answer you would like future users to see as the solution.

Well, it seems to have solved it but I need to test it out more. In a few days I will know if it solved it for sure, and then I will mark this