What do you mean by 'instances'. You can reduce the number of processes by opting out of the fission experiment. In about:config change the following preference to false. ''fission.autostart'' You probably need to restart the browser for that change to take effect. The browser should change the following preference to 3: ''fission.experiment.enrollmentStatus'' It is normal to have a number of processes. I have random RAM issues also. https://support.mozilla.org/en-US/kb/about-config-editor-firefox https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-or-cpu-resources https://support.mozilla.org/en-US/kb/task-manager-tabs-or-extensions-are-slowing-firefox