This usually the issue : 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. Further stuff can be done but what it is is undoing multiprocessor support and with ver 58 will be multi-thread. So I suggest not going down to 0 The above fix will cut 1/2 the ram use. Need to be monitoring what goes on in Windows Task Manager to get a understanding of what it is doing and what the changes are doing. 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. Hardware Acceleration might have also been a issue so turn it off. Run it later and see as you turn things back on and test it, and again. Restart Firefox after making these changes please. Update the Graphics Card Drivers, this is a must do. Firefox looks at the code then is CSS and out put as pixels so ya, Update. As for yours that is a unsupported Browser. Current Release Firefox 57.0 with a Full Version Installer https://www.mozilla.org/firefox/all/ 52.5.0 ESR is secure. It will continue to get security updates until May 2018, and you can download and install it from this page: https://www.mozilla.org/en-US/firefox/organizations/all/ <b>Note : Legacy Extensions will be deleted or removed in any version update after May 2018</b>. You should make a backup of your Profile before going back and just because: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles Please let us know if this solved your issue or if need further assistance.