Bug 412171, In <browser.xml>, 'Error: this.docShell is null', when the sidebar opens, r=myk+mconnor

browser/base/content/browser.xul

@@ -502,7 +502,7 @@
         <image id="sidebar-throbber"/>
         <toolbarbutton class="tabs-closebutton" tooltiptext="&sidebarCloseButton.tooltip;" oncommand="toggleSidebar();"/>
       </sidebarheader>
-      <browser id="sidebar" flex="1" autoscroll="false"
+      <browser id="sidebar" flex="1" autoscroll="false" disablehistory="true"
                 style="min-width: 14em; width: 18em; max-width: 36em;"/>
     </vbox>