If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block (wanted) content (e.g. Adblock Plus, NoScript, Ghostery, uBlock Origin) always make sure such extensions do not block (wanted) content. *make sure your extensions and filters are updated to the latest version Start Firefox in <u>Safe Mode</u> to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem. *switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance *do NOT click the "Refresh Firefox" button on the Safe Mode start window *https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode *https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems ---- Firefox 42+ has a Tracking Protection feature that is enabled by default in Private Browsing mode. Firefox can show a shield icon at the left end of the location/address bar that some content is blocked by Tracking Protection, click the shield icon for more information. You can disable this feature in "Options/Preferences -> Privacy" or via the <b>about:privatebrowsing</b> page that get when you open a New Private Window. *Options/Preferences -> Privacy: "Use Tracking Protection in Private Windows" *https://support.mozilla.org/en-US/kb/tracking-protection-firefox *https://support.mozilla.org/en-US/kb/control-center-site-privacy-and-security-firefox