Hi, try starting in Safe Mode by holding down Shift when you start Firefox. More - Diagnose Firefox issues using Troubleshoot Mode

If that doesn't help, you could try: Type about:config into the address bar, press Enter, accept the warning, scroll down and look for 'browser.tabs.remote.autostart' and 'browser.tabs.remote.autostart.2' If either or both exist, double click on either or both, to change 'Value' from True to False, then restart Firefox. More - https://support.mozilla.org/t5/Manage-preferences-and-add-ons/Configuration-Editor-for-Firefox/ta-p/35030

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Thanks. I will try it. If starting in safe mode works, do I need to do this all the time or is there a more permanent fix?

https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). If the problem goes away, that tells us one thing. If it does not, that tells us something else.

Thanks. The problem seems to have gone away in safe mode. What does that tell me?

If it's OK in Safe Mode, disable any theme or add-ons you have - Add-ons Manager (Ctrl+Shift+A) > Extensions/Appearance, then if it's still OK, re-enable them one by one until you find the culprit. Some may require a Firefox restart.

When multi-process windows in Firefox is enabled then Firefox will use more memory and may be less responsive. Try to disable multi-process windows in Firefox to see if that has effect.

You can disable multi-process windows in Firefox by setting these prefs to false on the about:config page.

• browser.tabs.remote.autostart = false
• browser.tabs.remote.autostart.2 = false

You can open the about:config page: via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

• http://www.ghacks.net/2016/07/22/multi-process-firefox/

You can try to disable hardware acceleration in Firefox.

• Options/Preferences -> Advanced -> General -> Browsing: "Use hardware acceleration when available"

You need to close and restart Firefox after toggling this setting.

• 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