Hi, yes is sparse. Please see if Accessibility Access is being allowed : Copy/Paste about:preferences#privacy to the Address Bar then Enter. Go down to Permissions and may sure that there is a check mark in the box Prevent accessibility services from accessing your browser.

If that was the case I would stop there and monitor after restarting Firefox. If not continue to here to the heading General --> Performance and untick everything. change the recommended size lower then see how it runs. Note: 1 = No Multiprocessor = slow again. Try 2 Restart Firefox after making these changes please. Note : Hardware Acceleration is for Video Card, Monitor to see if remain off or to turn back on.

You may also want to perform a scan for any Malware that maybe causing this issue :

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

Please let us know if this solved your issue or if need further assistance.

You can try to disable hardware acceleration in Firefox.

• Options/Preferences -> General: Performance
  remove checkmark: [ ] "Use recommended performance settings"
  remove checkmark: [ ] "Use hardware acceleration when available"
• https://support.mozilla.org/en-US/kb/performance-settings

Close and restart Firefox after modifying the setting to make the change effective.

• 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

• https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix