Added immediate saving of sidebar show/hide persist state. r=slamm

suite/common/sidebar/sidebarOverlay.js

@@ -231,6 +231,7 @@ function sidebarShowHide() {
     sidebar.setAttribute('hidden','true')
     sidebar_splitter.setAttribute('hidden','true')
   }
+  document.persist('sidebar-box', 'state')
 }
 
 function dumpAttributes(node) {

xpfe/components/sidebar/resources/sidebarOverlay.js

@@ -231,6 +231,7 @@ function sidebarShowHide() {
     sidebar.setAttribute('hidden','true')
     sidebar_splitter.setAttribute('hidden','true')
   }
+  document.persist('sidebar-box', 'state')
 }
 
 function dumpAttributes(node) {