I'm curious... how many windows and tabs do yo have open? You can set fission.autostart = false on the about:config page to opt-out of this experiment and disable Fission. You can open the about:config page via the location/address bar. You can click the button to "Accept the Risk and Continue". https://hacks.mozilla.org/2021/05/introducing-firefox-new-site-isolation-security-architecture/ https://support.mozilla.org/en-US/kb/performance-settings https://support.mozilla.org/en-US/kb/task-manager-tabs-or-extensions-are-slowing-firefox