Please consider turning on send info to Mozilla before posting a question. This helps us help you. As I have no info from your system that would help see things that cause issues. No idea what version Firefox you are running other that 56 So try to update to current version 56.0.2 https://support.mozilla.org/en-US/kb/update-firefox-latest-version alternative is to uninstall then https://www.mozilla.org/firefox/all/ Full Version Installer also https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems?redirectlocale=en-US&redirectslug=Troubleshooting+extensions+and+themes Check to : See if Multi-Processor Support is turned on. Multi-processor support feature may be disabled depending on your setup (it was for me) - 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 "0/1", then that means it's disabled. 0/2 and higher = on unless says it is off. Then check the Task Manager and see how many instances of Firefox is running and what the memory numbers are like. If need to can turn off multiprocessor : You can try to modify multi-process settings to see if this has effect. 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. 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 http://kb.mozillazine.org/about:config Also can reverse everything this tells you to enable it. http://www.ghacks.net/2016/07/22/multi-process-firefox/ Please let us know if this solved your issue or if need further assistance.