Hi ! We've had may of these reports lately - if all goes well this will be fixed when Firefox 57 is released. For now, you could do this : Type in the address bar '''about:config''' (press Enter) Promise to be careful, if asked) Type and look for the preference : '''security.sandbox.content.level''' and set its value to '''1''' (one) (default value is 3 ) Then close and restart Firefox. Note : Don't forget to change the value back once this is fixed.