Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

I don't have any add-ons or extensions. I removed Firefox and reinstalled it but the problem is still there.

So it still happens in Troubleshoot Mode ?

Yes. There is no difference when in troubleshoot mode - still negatives.

Does it still happen in a new profile? An easy way to test a new profile is to install Developer Edition and see if it happens there or refresh your existing profile. Make sure you stay signed out of your sync account when testing.

I downloaded the Developer Edition and the YouTube videos are normal, not negatives. What does this mean? Do i just use the Developer Edition as my browser?

You can create a new profile as a quick test to see if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

If the new profile works, you can transfer files from a previously used profile to the new profile, but be careful not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

I created a new profile, closed and restarted Firefox. When I reopened the profile manager, it found the new profile and said that the new one was "the profile in use and cannot be deleted". Nothing has changed everything is still negative.