It could be funny if...

gistfile1.js

let AddonsMgrListener = {
  get addonBar() document.getElementById("addon-bar"),
  get statusBar() document.getElementById("status-bar"),
  getAddonBarItemCount: function() {
    // Take into account the contents of the status bar shim for the count.
    var itemCount = this.statusBar.childNodes.length;

    var defaultOrNoninteractive = this.addonBar.getAttribute("defaultset")
                                      .split(",")
                                      .concat(["separator", "spacer", "spring"]);
    this.addonBar.currentSet.split(",").forEach(function (item) {
      if (defaultOrNoninteractive.indexOf(item) == -1)
        itemCount++;
    });

    return itemCount;
  },
  onInstalling: function(aAddon) {
    this.lastAddonBarCount = this.getAddonBarItemCount();
  },
  onInstalled: function(aAddon) {
    if (this.getAddonBarItemCount() > this.lastAddonBarCount)
      setToolbarVisibility(this.addonBar, true);
  },
  onUninstalling: function(aAddon) {
    this.lastAddonBarCount = this.getAddonBarItemCount();
  },
  onUninstalled: function(aAddon) {
    if (this.getAddonBarItemCount() == 0)
      setToolbarVisibility(this.addonBar, false);
  },
  onEnabling: function(aAddon) this.onInstalling(),
  onEnabled: function(aAddon) this.onInstalled(),
  onDisabling: function(aAddon) this.onUninstalling(),
  onDisabled: function(aAddon) this.onUninstalled(),
};

function toggleAddonBar() {
  let addonBar = document.getElementById("addon-bar");
  setToolbarVisibility(addonBar, addonBar.collapsed);
}

var Scratchpad = {
  prefEnabledName: "devtools.scratchpad.enabled",

  openScratchpad: function SP_openScratchpad() {
    const SCRATCHPAD_WINDOW_URL = "chrome://browser/content/scratchpad.xul";
    const SCRATCHPAD_WINDOW_FEATURES = "chrome,titlebar,toolbar,centerscreen,resizable,dialog=no";

    return Services.ww.openWindow(null, SCRATCHPAD_WINDOW_URL, "_blank",
                                  SCRATCHPAD_WINDOW_FEATURES, null);
  },
};

var StyleEditor = {
  prefEnabledName: "devtools.style_editor.enabled",
  openChrome: function SE_openChrome() {
    const WINDOW_URL = "chrome://browser/content/StyleEditor/StyleEditorChrome.xul";
    const WINDOW_FLAGS = "chrome,titlebar,toolbar,centerscreen,resizable,dialog=no";
    return Services.ww.openWindow(null, WINDOW_URL, "_blank", WINDOW_FLAGS, null);
  }
};

XPCOMUtils.defineLazyGetter(window, "gShowPageResizers", function () {
#ifdef XP_WIN
  // Only show resizers on Windows 2000 and XP
  let sysInfo = Components.classes["@mozilla.org/system-info;1"]
                          .getService(Components.interfaces.nsIPropertyBag2);
  return parseFloat(sysInfo.getProperty("version")) < 6;
#else
  return false;
#endif
});