Here Are some screenshots and I am using only 2 tabs one is facebook and second one is youtube on which nothing is being played.

Please make sure that Accessibility Services are checked to Block and as navigation for your browser : http://kb.mozillazine.org/Menu_differences_in_Windows,_Linux,_and_Mac for Windows Direction below. and to make changes here : You could try this please : Go the 3 Bar Menu then Options --> 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 : Acceleration is for your Video Card, monitor to see if need to turn back on. https://support.mozilla.org/en-US/kb/performance-settings Please let us know if this solved your issue or if need further assistance

It surely reduced RAM Usage but CPU usage is above 200 and almost 300 %