gecko-dev/xpfe/browser/resources/content/navWidgets.css

box[type="location-field"]
  {
    -moz-binding          : url("chrome://navigator/content/navWidgetBindings.xml#urlbar");
  }
  
menulist[editable="true"]
  {
    -moz-binding          : url("chrome://navigator/content/navWidgetBindings.xml#menulist-editable");
  }  
  
.location-field
  {
    -moz-binding          : url("chrome://navigator/content/navWidgetBindings.xml#urlbar-menulist");
    -moz-user-focus       : ignore;
  }  
  
/* XXX factor me */
.textfield-input
  {
    -moz-user-focus       : normal;
  }