fix sidebar middle click

browser/base/content/browser.xul

@@ -1050,7 +1050,7 @@
         <spacer flex="1"/>
         <toolbarbutton class="tabs-closebutton" oncommand="toggleSidebar();"/>      
       </sidebarheader>        
-      <browser id="sidebar" flex="1"
+      <browser id="sidebar" flex="1" autoscroll="false"
                style="min-width: 150px; width: 200px; max-width: 400px;"/>
     </vbox>