Please update to 57.0.2 for fixes https://support.mozilla.org/en-US/kb/update-firefox-latest-version Check to see if fix took : Go to the Firefox 3 Bar Menu --> Help ? --> Troubleshooting Information Page and take a look in the Accessibility section if accessibility is set to "true" there. if yes, go to the Firefox 3 Bar Menu --> Options --> Privacy & Security panel and under Permissions check the setting to Prevent Accessibility Services from accessing your browser. Restart Firefox Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox. A small dialog should appear. Click Start In Safe Mode (not Refresh). TEST , as no extensions working now. Is the problem still there? Each extension maybe 20megs of ram. https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding 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 If still issues : You could try this please : Go the Menu then Tools --> Options --> Performance and untick everything. change the recommended size lower then see how it runs. Note: 0 = No Multi-proccesor = slow again. TRY 2 Restart Firefox after making these changes please. https://www.howtogeek.com/332449/whats-new-in-firefox-quantum/ Update Video Card Drivers. Please let us know if this solved your issue or if need further assistance.