Please consider turning on send info to Mozilla before posting a question. This helps us help you. I have no info because the above was turned off. So it could be one of hundreds of things. Below would have shown up if was turned on...... You may have volunteered for this Mozilla experiment. 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, just like this Safe Browsing version 4 (at the end of the experiment they will be disabled anyway). See for further information : https://support.mozilla.org/en-US/kb/shield 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. If see 0.2 or greater it is turned on. copy/paste to address bar then enter about:config 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. You will have to work backwards with the info I give you to turn it off. You can try to modify multi-process settings to see if this has effect. set (copy/past to search bar in about:config) edom.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. (copy/past below to search bar in about:config) browser.tabs.remote.autostart = false browser.tabs.remote.autostart.2 = false http://kb.mozillazine.org/about:config http://www.ghacks.net/2016/07/22/multi-process-firefox/ Ok, so that's all am going to give you to check on. Note : Firefox 56.0.2 is current release https://www.mozilla.org/firefox/all/ Full Version Installer Note : Firefox 57 Quantum release date Nov 14th https://www.mozilla.org/en-US/firefox/quantum/ Note : Legacy Extensions will be disabled and or removed. Please let us know if this solved your issue or if need further assistance.