Toolbar button can't be placed on Navigation Toolbar in Firefox 29+ (Australis)

[Infocatcher]

No description provided.

[Infocatcher]

Also there is a bug with
resource:///modules/CustomizableUI.jsm

  getUnusedWidgets: function(aWindowPalette) {
    ...
    for (let node of aWindowPalette.children) {
      LOG("In palette children: " + node.id);
      if (node.id && !this.getPlacementOfWidget(node.id)) {
        widgets.add(node.id);
      }
    }

  getPlacementOfWidget: function(aWidgetId, aOnlyRegistered) {
    ...
    for (let [area, placements] of gPlacements) {
      let index = placements.indexOf(aWidgetId);
      if (index != -1) {
        return { area: area, position: index };
      }
    }

    return null;
  },

If something went wrong, buttons from restartless extensions may disappear at all (still in palette, but not visible in UI).

Ugly workaround:

var scope = Cu.import("resource:///modules/CustomizableUI.jsm", {});
var gPlacements = scope.gPlacements;
//gPlacements.clear();
for(var [area, placements] of scope.gPlacements) {
    var toolbar = document.getElementById(area);
    if(!toolbar || toolbar.localName != "toolbar")
        continue;
    gPlacements.set(area, toolbar.currentSet.split(","));
}
scope.gDirty = true;
scope.CustomizableUIInternal.saveState();

(and restart)
This will be saved in browser.uiCustomization.state.