diff --git a/common/locale/en-US/gui.xml b/common/locale/en-US/gui.xml
index 02afea01..94a34def 100644
--- a/common/locale/en-US/gui.xml
+++ b/common/locale/en-US/gui.xml
@@ -208,6 +208,20 @@
         </p>
     </description>
 </item>
+<item>
+    <spec>:sidebar! <oa>name</oa></spec>
+    <description>
+        <p>
+            Toggle the sidebar window. When <oa>name</oa> is provided, the
+            semantics are as follows: If the named is currently open, it is
+            closed. Otherwise the sidebar is closed. When <oa>name</oa> is
+            not provided, the semantics are as follows: If the sidebar is
+            currently open, it is closed. Otherwise the previously open sidebar
+            panel is re-opened.
+        </p>
+    </description>
+</item>
+
 
 <h2 tag="status-line status-bar">Status line</h2>
 
diff --git a/common/modules/util.jsm b/common/modules/util.jsm
index c67b8f37..52debe7a 100644
--- a/common/modules/util.jsm
+++ b/common/modules/util.jsm
@@ -743,15 +743,14 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
      * @param {function(XMLHttpRequest)} callback
      * @returns {XMLHttpRequest}
      */
-    httpGet: function httpGet(url, callback) {
+    httpGet: function httpGet(url, callback, self) {
         try {
             let xmlhttp = services.Xmlhttp();
             xmlhttp.mozBackgroundRequest = true;
-            if (callback)
-                xmlhttp.onreadystatechange = function () {
-                    if (xmlhttp.readyState == 4)
-                        callback(xmlhttp);
-                };
+            if (callback) {
+                xmlhttp.onload = function handler(event) { util.trapErrors(callback, self, xmlhttp, event) };
+                xmlhttp.onerror = xmlhttp.onload;
+            }
             xmlhttp.open("GET", url, !!callback);
             xmlhttp.send(null);
             return xmlhttp;
diff --git a/pentadactyl/NEWS b/pentadactyl/NEWS
index c1d125e3..578f3d62 100644
--- a/pentadactyl/NEWS
+++ b/pentadactyl/NEWS
@@ -80,6 +80,8 @@
       - :saveas now provides completions for default file names, and
         automatically chooses a filename when the save target is a
         directory.
+      - :sidebar now accepts a ! flag to toggle the sidebar rather
+        than open it unconditionally.
       - Added :write !cmd and :write >>file.
       - Added :yank command.
       - :delmarks, :marks and :qmarks now also accept ranges, same as
diff --git a/pentadactyl/content/config.js b/pentadactyl/content/config.js
index 4df9288c..bed5b294 100644
--- a/pentadactyl/content/config.js
+++ b/pentadactyl/content/config.js
@@ -167,7 +167,7 @@ var Config = Module("config", ConfigBase, {
 }, {
 }, {
     commands: function (dactyl, modules, window) {
-        const { commands, completion } = modules;
+        const { commands, completion, config } = modules;
         const { document } = window;
 
         commands.add(["winon[ly]"],
@@ -205,10 +205,20 @@ var Config = Module("config", ConfigBase, {
             "Open the sidebar window",
             function (args) {
                 function compare(a, b) util.compareIgnoreCase(a, b) == 0
+                let title = document.getElementById("sidebar-title");
+
+                dactyl.assert(args.length || title.value || args.bang && config.lastSidebar,
+                              "Argument required");
+
+                if (!args.length)
+                    return window.toggleSidebar(title.value ? null : config.lastSidebar);
 
                 // focus if the requested sidebar is already open
-                if (compare(document.getElementById("sidebar-title").value, args[0]))
+                if (compare(title.value, args[0])) {
+                    if (args.bang)
+                        return window.toggleSidebar();
                     return dactyl.focus(document.getElementById("sidebar-box"));
+                }
 
                 let menu = document.getElementById("viewSidebarMenu");
 
@@ -223,7 +233,8 @@ var Config = Module("config", ConfigBase, {
                 return dactyl.echoerr("No sidebar " + args[0] + " found");
             },
             {
-                argCount: "1",
+                argCount: "?",
+                bang: true,
                 completer: function (context) {
                     context.ignoreCase = true;
                     return completion.sidebar(context);
@@ -322,6 +333,12 @@ var Config = Module("config", ConfigBase, {
             "Firefox location bar entries (bookmarks and history sorted in an intelligent way)",
             completion.location);
     },
+    events: function (dactyl, modules, window) {
+        modules.events.addSessionListener(window, "SidebarFocused", function (event) {
+            modules.config.lastSidebar = window.document.getElementById("sidebar-box")
+                                               .getAttribute("sidebarcommand");
+        }, false);
+    },
     modes: function (dactyl, modules, window) {
         const { config, modes } = modules;
         config.ignoreKeys = {