browser.tabs.remote.autostart = false
  browser.tabs.remote.autostart.2 = false 
  http://www.ghacks.net/2016/07/22/multi-process-firefox/ 

  http://kb.mozillazine.org/about:config

I actually asked this same question in January, the suggested solution worked then but won't work now. This problem has occurred once again, and when I went into the about:config page to repeat the process I discovered that these options were already set to false, and I'm still having the problem. Now I'm lost. Also, I am not getting any error messages this time. I did try to uninstall and reinstall multifox, but after I uninstalled it, I couldn't find it again to reinstall. The following is the reply that ultimately worked and solved my problem last time, You can disable multi-process tabs in Firefox by setting the related prefs to false on the about:config page. browser.tabs.remote.autostart = false browser.tabs.remote.autostart.2 = false http://www.ghacks.net/2016/07/22/multi-process-firefox/ You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue. http://kb.mozillazine.org/about:config