Am running multi tabs on high end cpu with tons of ram and Task Manager shows am running 1 0f 3 cores 2 showing both at about 1,105.9 MB plus some add-ons with more ram... Please report back about yours. https://www.ghacks.net/2016/07/22/multi-process-firefox/ and https://www.ghacks.net/2016/02/15/change-how-many-processes-multi-process-firefox-uses/ Also try : about studies in the address bar as per 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, https://support.mozilla.org/en-US/kb/shield Oh if Firefox just updated to 56.0.1 sometimes a reboot is need as that happened to mine like was using 500megs, reboot no issue. Please let us know if this solved your issue or if need further assistance.