I could be the system is having issues with the RAM. https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-ram https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding https://support.mozilla.org/en-US/kb/firefox-takes-long-time-start-up https://support.mozilla.org/en-US/kb/quick-fixes-if-your-firefox-slows-down https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-or-cpu-resources MemTest Could you please run a tool from http://memtest.org/ in order to check the integrity of your RAM? You will need a thumb or disk drive to install it on. Do you let Windows handle the page file or did you set a fixed size ? Control Panel -> System -> Advanced -> Performance -> Settings If you use a fixed size for the page file then try the former and let Windows handle the page file. [https://docs.microsoft.com/en-us/windows/client-management/determine-appropriate-page-file-size#:~:text=Support%20for%20system%20crash%20dumps%20%20%20,on%20kernel%20virtual%20memory%20usage.%20%20...%20 How to determine the appropriate page file size for 64-bit versions of Windows] {web link}

You can check the Firefox Task Manager (about:performance) and about:memory and about:processes pages. *https://support.mozilla.org/en-US/kb/task-manager-tabs-or-extensions-are-slowing-firefox *https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-or-cpu-resources ---- Start Firefox in <b>Troubleshoot Mode</b> to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if <b>hardware acceleration</b> or <b>userChrome.css</b> is causing the problem. *switch to the DEFAULT 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