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 "Refresh Firefox" in 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

Make sure you allow pages to choose their own colors as this affects background images.

• Settings -> General -> Language and Appearance -> Colors -> Manage Colors
  "Override the colors specified by the page with your selections above"

Try "Never" if the default "Only with High Contrast themes" isn't working.

• https://support.mozilla.org/en-US/kb/disable-high-contrast-mode-firefox

Troubleshoot mode helped me identify the issue in that it disabled the extensions in the browser. Turned out it was the Ghostery tracker and ad-blocker extension that was the villain. There doesn't seem to be a setting in ghostery where I can stop this. However now I know what the issue is it's not now an itch I need to scratch. Like finding the horrendous nuisance of a rattle in a car, once you know it doesn't seem to be so annoying.

Thank you for the help. Good stuff.