Such nice way to greet Support Volunteers.

You do not have send info to Mozilla ticked so I have no information that can pin point the issue for you. Next time please think about turning it on before sending a help request.

With that said it can be a number of things Multi-processor issue or your enrolled in Mozilla programs in a test. For the Test Program extension part of a Mozilla experiment, called 'Shield Studies'. Without even knowing it, you may have volunteered for this Mozilla experiment. Would you go to : Options => Privacy & Security => under 'Data Collection and Use' : Did you uncheck : 'Allow Firefox to install and run studies ' or is it checked  ?

To check if you are enrolled in these studies : Type in the address bar about:studies Any extensions that you see listed there, you can either disable or remove, ie : Safe Browsing version 4 (and at the end of the experiment they will be disabled anyway). See for further information : https://support.mozilla.org/en-US/kb/shield As there are a couple of others.

See if Multi-Processor Support is turned on. Multi-processor support feature may be disabled enabled on your setup - you can check this by launching Firefox, then enter in "about:support" in the address bar; near the bottom, you should see a heading that says: "Multiprocess Windows", then look at the value next to it. If it says "0/2" (or more), then that means it's enabled. You can try to modify multi-process settings to see if this has effect.

   set dom.ipc.processCount to 1 if it is currently set to a higher value (4)
   disable multi-process windows in Firefox 

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 accept the risk!" to continue.

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

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

While in about:support please click the Memory line then the first memory button and look in the report for a line or 2 that says Ghost Addresses /URL's If you find these please close all open tabs and hit refresh several times. This will clear those out. You may have to do this again, if memory use gets large just close tabs hit refresh. It is a bug.

Try : https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix and https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems?redirectlocale=en-US&redirectslug=Troubleshooting+extensions+and+themes

So once again with out the send info to Mozilla ticked before you send a report I am shooting blind at multiple possible issues.

So the current version of Firefox is 56.02 https://www.mozilla.org/firefox/all/ So you could uninstall and reinstall from above URL the Full Version Installer.

Note : Firefox 57 Quantum release date Nov 14th https://www.mozilla.org/en-US/firefox/quantum/ Note : All Legacy Extensions will be disabled or deleted

Thank you for your patience.

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

May I also suggest if possible to update your Graphics Card Drivers, Motherboard drivers especially. If can go to the motherboard makers web site and find support/drivers if they still have them as they take them down after a few years.

You will find the makers name and model # on the motherboard or can run a program called CPU-Z and that will list make and model.

Having updated drivers will help. There are driver update programs but you do take a risk.

Note: Windows 10 can and will change your hardware Drivers to Microsoft's https://www.howtogeek.com/302595/how-to-stop-windows-10-from-automatically-updating-hardware-drivers/

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