Index: wp-admin/includes/ajax-actions.php
===================================================================
--- wp-admin/includes/ajax-actions.php	(revision 23658)
+++ wp-admin/includes/ajax-actions.php	(working copy)
@@ -1050,9 +1050,9 @@
 
 	$id = $revision_id = 0;
 
-	$post_ID = (int) $_POST['post_ID'];
-	$_POST['ID'] = $post_ID;
-	$post = get_post($post_ID);
+	$post_id = (int) $_POST['post_id'];
+	$_POST['ID'] = $_POST['post_ID'] = $post_id;
+	$post = get_post($post_id);
 	if ( 'auto-draft' == $post->post_status )
 		$_POST['post_status'] = 'draft';
 
@@ -1068,10 +1068,10 @@
 	}
 
 	if ( 'page' == $post->post_type ) {
-		if ( !current_user_can('edit_page', $post_ID) )
+		if ( !current_user_can('edit_page', $post->ID) )
 			wp_die( __( 'You are not allowed to edit this page.' ) );
 	} else {
-		if ( !current_user_can('edit_post', $post_ID) )
+		if ( !current_user_can('edit_post', $post->ID) )
 			wp_die( __( 'You are not allowed to edit this post.' ) );
 	}
 
Index: wp-admin/includes/misc.php
===================================================================
--- wp-admin/includes/misc.php	(revision 23658)
+++ wp-admin/includes/misc.php	(working copy)
@@ -586,3 +586,30 @@
 	return $response;
 }
 add_filter( 'heartbeat_received', 'wp_check_locked_posts', 10, 2 );
+
+/**
+ * Output the HTML for restoring the post data from DOM storage
+ *
+ * @since 3.6
+ * @access private
+ */
+function _local_storage_notice() {
+	global $current_screen;
+
+	if ( empty($current_screen) || 'post' != $current_screen->id )
+		return;
+
+	?>
+	<div id="local-storage-notice" class="hidden">
+	<p class="local-restore">
+		<?php _e('The backup of this post in your browser is different from the version below.'); ?>
+		<a class="restore-backup" href="#"><?php _e('Restore the backup.'); ?></a>
+	</p>
+	<p class="undo-restore hidden">
+		<?php _e('Post restored successfully.'); ?>
+		<a class="undo-restore-backup" href="#"><?php _e('Undo.'); ?></a>
+	</p>
+	</div>
+	<?php
+}
+add_action( 'admin_footer', '_local_storage_notice' );
Index: wp-includes/js/admin-bar.js
===================================================================
--- wp-includes/js/admin-bar.js	(revision 23658)
+++ wp-includes/js/admin-bar.js	(working copy)
@@ -132,6 +132,18 @@
 				}, 100);
 			}
 		});
+
+		// Empty sessionStorage on logging out
+		if ( 'sessionStorage' in window ) {
+			$('#wp-admin-bar-logout a').click( function() {
+				try {
+					for ( var key in sessionStorage ) {
+						if ( key.indexOf('wp-autosave-') != -1 )
+							sessionStorage.removeItem(key);
+					}
+				} catch(e) {}
+			});
+		}
 	});
 } else {
 	(function(d, w) {
@@ -310,6 +322,17 @@
 				addEvent(aB, 'click', function(e) {
 					scrollToTop( e.target || e.srcElement );
 				});
+
+				addEvent( document.getElementById('wp-admin-bar-logout'), 'click', function() {
+					if ( 'sessionStorage' in window ) {
+						try {
+							for ( var key in sessionStorage ) {
+								if ( key.indexOf('wp-autosave-') != -1 )
+									sessionStorage.removeItem(key);
+							}
+						} catch(e) {}
+					}
+				});
 			}
 
 			if ( w.location.hash )
Index: wp-includes/js/autosave.js
===================================================================
--- wp-includes/js/autosave.js	(revision 23658)
+++ wp-includes/js/autosave.js	(working copy)
@@ -187,6 +187,7 @@
 function autosave_saved_new(response) {
 	blockSave = false;
 	var res = autosave_parse_response(response), postID;
+
 	if ( res && res.responses.length && !res.errors ) {
 		// An ID is sent only for real auto-saves, not for autosave=0 "keepalive" saves
 		postID = parseInt( res.responses[0].id, 10 );
@@ -257,77 +258,21 @@
 
 	autosave_disable_buttons();
 
-	post_data = {
-		action: "autosave",
-		post_ID:  jQuery("#post_ID").val() || 0,
-		autosavenonce: jQuery('#autosavenonce').val(),
-		post_type: jQuery('#post_type').val() || "",
-		autosave: 1
-	};
+	post_data = wp.autosave.getPostData();
 
-	jQuery('.tags-input').each( function() {
-		post_data[this.name] = this.value;
-	} );
-
 	// We always send the ajax request in order to keep the post lock fresh.
 	// This (bool) tells whether or not to write the post to the DB during the ajax request.
-	doAutoSave = true;
+	doAutoSave = post_data.autosave;
 
 	// No autosave while thickbox is open (media buttons)
 	if ( jQuery("#TB_window").css('display') == 'block' )
 		doAutoSave = false;
 
-	/* Gotta do this up here so we can check the length when tinymce is in use */
-	if ( rich && doAutoSave ) {
-		ed = tinymce.activeEditor;
-		// Don't run while the tinymce spellcheck is on. It resets all found words.
-		if ( ed.plugins.spellchecker && ed.plugins.spellchecker.active ) {
-			doAutoSave = false;
-		} else {
-			if ( 'mce_fullscreen' == ed.id || 'wp_mce_fullscreen' == ed.id )
-				tinymce.get('content').setContent(ed.getContent({format : 'raw'}), {format : 'raw'});
-			tinymce.triggerSave();
-		}
-	}
-
-	if ( fullscreen && fullscreen.settings.visible ) {
-		post_data["post_title"] = jQuery('#wp-fullscreen-title').val() || '';
-		post_data["content"] = jQuery("#wp_mce_fullscreen").val() || '';
-	} else {
-		post_data["post_title"] = jQuery("#title").val() || '';
-		post_data["content"] = jQuery("#content").val() || '';
-	}
-
-	if ( jQuery('#post_name').val() )
-		post_data["post_name"] = jQuery('#post_name').val();
-
 	// Nothing to save or no change.
 	if ( ( post_data["post_title"].length == 0 && post_data["content"].length == 0 ) || post_data["post_title"] + post_data["content"] == autosaveLast ) {
 		doAutoSave = false;
 	}
 
-	origStatus = jQuery('#original_post_status').val();
-
-	goodcats = ([]);
-	jQuery("[name='post_category[]']:checked").each( function(i) {
-		goodcats.push(this.value);
-	} );
-	post_data["catslist"] = goodcats.join(",");
-
-	if ( jQuery("#comment_status").prop("checked") )
-		post_data["comment_status"] = 'open';
-	if ( jQuery("#ping_status").prop("checked") )
-		post_data["ping_status"] = 'open';
-	if ( jQuery("#excerpt").size() )
-		post_data["excerpt"] = jQuery("#excerpt").val();
-	if ( jQuery("#post_author").size() )
-		post_data["post_author"] = jQuery("#post_author").val();
-	if ( jQuery("#parent_id").val() )
-		post_data["parent_id"] = jQuery("#parent_id").val();
-	post_data["user_ID"] = jQuery("#user-id").val();
-	if ( jQuery('#auto_draft').val() == '1' )
-		post_data["auto_draft"] = '1';
-
 	if ( doAutoSave ) {
 		autosaveLast = post_data["post_title"] + post_data["content"];
 		jQuery(document).triggerHandler('wpcountwords', [ post_data["content"] ]);
@@ -350,3 +295,370 @@
 		success: successCallback
 	});
 }
+
+// Autosave in localStorage
+// set as simple object/mixin for now
+window.wp = window.wp || {};
+wp.autosave = wp.autosave || {};
+
+(function($){
+// Returns the data for saving in both localStorage and autosaves to the server
+wp.autosave.getPostData = function() {
+	var ed = typeof tinymce != 'undefined' ? tinymce.activeEditor : null, post_name, parent_id, cats = [],
+		data = {
+			action: 'autosave',
+			autosave: true,
+			post_id: $('#post_ID').val() || 0,
+			autosavenonce: $('#autosavenonce').val() || '',
+			post_type: $('#post_type').val() || '',
+			post_author: $('#post_author').val() || '',
+			excerpt: $('#excerpt').val() || ''
+		};
+
+	if ( ed && !ed.isHidden() ) {
+		// Don't run while the tinymce spellcheck is on. It resets all found words.
+		if ( ed.plugins.spellchecker && ed.plugins.spellchecker.active ) {
+			data.autosave = false;
+			return data;
+		} else {
+			if ( 'mce_fullscreen' == ed.id )
+				tinymce.get('content').setContent(ed.getContent({format : 'raw'}), {format : 'raw'});
+
+			tinymce.triggerSave();
+		}
+	}
+
+	if ( typeof fullscreen != 'undefined' && fullscreen.settings.visible ) {
+		data['post_title'] = $('#wp-fullscreen-title').val() || '';
+		data['content'] = $('#wp_mce_fullscreen').val() || '';
+	} else {
+		data['post_title'] = $('#title').val() || '';
+		data['content'] = $('#content').val() || '';
+	}
+
+	/*
+	// We haven't been saving tags with autosave since 2.8... Start again?
+	$('.the-tags').each( function() {
+		data[this.name] = this.value;
+	});
+	*/
+
+	$('input[id^="in-category-"]:checked').each( function() {
+		cats.push(this.value);
+	});
+	data['catslist'] = cats.join(',');
+
+	if ( post_name = $('#post_name').val() )
+		data['post_name'] = post_name;
+
+	if ( parent_id = $('#parent_id').val() )
+		data['parent_id'] = parent_id;
+
+	if ( $('#comment_status').prop('checked') )
+		data['comment_status'] = 'open';
+
+	if ( $('#ping_status').prop('checked') )
+		data['ping_status'] = 'open';
+
+	if ( $('#auto_draft').val() == '1' )
+		data['auto_draft'] = '1';
+
+	return data;
+}
+
+wp.autosave.local = {
+
+	lastsaveddata: '',
+	blog_id: 0,
+	ajaxurl: window.ajaxurl || 'wp-admin/admin-ajax.php',
+	hasStorage: false,
+
+	// Check if the browser supports sessionStorage and it's not disabled
+	checkStorage: function() {
+		var test = Math.random(), result = false;
+
+		try {
+			sessionStorage.setItem('wp-test', test);
+			result = sessionStorage.getItem('wp-test') == test;
+			sessionStorage.removeItem('wp-test');
+		} catch(e) {}
+
+		this.hasStorage = result;
+		return result;
+    },
+
+	/**
+	 * Initialize the local storage
+	 *
+	 * @return mixed False if no sessionStorage in the browser or an Object containing all post_data for this blog
+	 */
+	getStorage: function() {
+		var stored_obj = false;
+		// Separate local storage containers for each blog_id
+		if ( this.hasStorage && this.blog_id ) {
+			stored_obj = sessionStorage.getItem( 'wp-autosave-' + this.blog_id );
+
+			if ( stored_obj )
+				stored_obj = JSON.parse( stored_obj );
+			else
+				stored_obj = {};
+		}
+
+		return stored_obj;
+	},
+
+	/**
+	 * Set the storage for this blog
+	 *
+	 * Confirms that the data was saved successfully.
+	 *
+	 * @return bool
+	 */
+	setStorage: function( stored_obj ) {
+		var key;
+
+		if ( this.hasStorage && this.blog_id ) {
+			key = 'wp-autosave-' + this.blog_id;
+			sessionStorage.setItem( key, JSON.stringify( stored_obj ) );
+			return sessionStorage.getItem( key ) !== null;
+		}
+
+		return false;
+	},
+
+	/**
+	 * Get the saved post data for the current post
+	 *
+	 * @return mixed False if no storage or no data or the post_data as an Object
+	 */
+	getData: function() {
+		var stored = this.getStorage(), post_id = $('#post_ID').val();
+
+		if ( !stored || !post_id )
+			return false;
+
+		return stored[ 'post_' + post_id ] || false;
+	},
+
+	/**
+	 * Set (save) post data in the storage
+	 *
+	 * @return bool
+	 */
+	setData: function( stored_data ) {
+		var stored = this.getStorage(), post_id = $('#post_ID').val();
+
+		if ( !stored || !post_id )
+			return false;
+
+		stored[ 'post_' + post_id ] = stored_data;
+
+		return this.setStorage(stored);
+	},
+
+	/**
+	 * Save post data for the current post
+	 *
+	 * Runs on a 15 sec. schedule, saves when there are differences in the post title or content.
+	 * When the optional data is provided, updates the last saved post data.
+	 *
+	 * $param data optional Object The post data for saving, minimum 'post_title' and 'content'
+	 * @return bool
+	 */
+	save: function( data ) {
+		var result = false;
+
+		if ( ! data ) {
+			post_data = wp.autosave.getPostData();
+		} else {
+			post_data = this.getData() || {};
+			$.extend( post_data, data );
+		}
+
+		// If the content and title are empty or did not change since the last save, don't save again
+		if ( post_data.post_title + ': ' + post_data.content == this.lastsaveddata )
+			return false;
+
+		// Cannot get the post data at the moment
+		if ( !post_data.autosave )
+			return false;
+
+		post_data['save_time'] = (new Date()).getTime();
+		post_data['status'] = $('#post_status').val() || '';
+		result = this.setData( post_data );
+
+		if ( result )
+			this.lastsaveddata = post_data.post_title + ': ' + post_data.content;
+
+		return result;
+	},
+
+	// Initialize and run checkPost() on loading the script (before TinyMCE init)
+	init: function( settings ) {
+		var self = this;
+
+		// Run only on the Add/Edit Post screens and in browsers that have sessionStorage
+		if ( 'post' != window.pagenow || ! this.checkStorage() )
+			return;
+		// editor.js has to be loaded before autosave.js
+		if ( typeof switchEditors == 'undefined' )
+			return;
+
+		if ( settings )
+			$.extend( this, settings );
+
+		if ( !this.blog_id )
+			this.blog_id = typeof window.autosaveL10n != 'undefined' ? window.autosaveL10n.blog_id : 0;
+
+		this.checkPost();
+		$(document).ready( self.run );
+	},
+
+	// Run on DOM ready
+	run: function() {
+		var self = this, post_data;
+
+		// Set the comparison string
+		if ( !this.lastsaveddata ) {
+			post_data = wp.autosave.getPostData();
+
+			if ( post_data.content && $('#wp-content-wrap').hasClass('tmce-active') )
+				this.lastsaveddata = post_data.post_title + ': ' + switchEditors.pre_wpautop( post_data.content );
+			else
+				this.lastsaveddata = post_data.post_title + ': ' + post_data.content;
+		}
+
+		// Set the schedule
+		this.schedule = $.schedule({
+			time: 15 * 1000,
+			func: function() { wp.autosave.local.save(); },
+			repeat: true,
+			protect: true
+		});
+
+		$('form#post').on('submit.autosave-local', function() {
+			var editor = typeof tinymce != 'undefined' && tinymce.get('content');
+
+			if ( editor && ! editor.isHidden() ) {
+				// Last onSubmit event in the editor, needs to run after the content has been moved to the textarea.
+				editor.onSubmit.add( function() {
+					wp.autosave.local.save({
+						post_title: $('#title').val() || '',
+						content: $('#content').val() || '',
+						excerpt: $('#excerpt').val() || ''
+					});
+				});
+			} else {
+				self.save({
+					post_title: $('#title').val() || '',
+					content: $('#content').val() || '',
+					excerpt: $('#excerpt').val() || ''
+				});
+			}
+		});
+	},
+
+	// Strip whitespace and compare two strings
+	compare: function( str1, str2 ) {
+		function strip_space( string ) {
+			return string.toString().replace(/[\x20\t\r\n\f]+/g, '');
+		}
+
+		return ( strip_space( str1 || '' ) == strip_space( str2 || '' ) );
+	},
+
+	/**
+	 * Check if the saved data for the current post (if any) is different than the loaded post data on the screen
+	 *
+	 * Shows a standard message letting the user restore the post data if different.
+	 *
+	 * @return void
+	 */
+	checkPost: function() {
+		var self = this, post_data = this.getData(), content, match = false, check_data, notice;
+
+		if ( post_data ) {
+			content = $('#content').val();
+			check_data = $.extend( {}, post_data );
+
+			if ( $('#wp-content-wrap').hasClass('tmce-active') )
+				content = switchEditors.pre_wpautop( content );
+
+			if ( this.compare( content, check_data.content ) && this.compare( $('#title').val(), check_data.post_title ) && this.compare( $('#excerpt').val(), check_data.excerpt ) )
+				match = true;
+
+			if ( ! match ) {
+				// We have three choices here:
+				// - Do an autosave and then show the standard notice "There is an autosave newer than...".
+				// - Offer to load/restore the backed up post data.
+				// - Restore the post_data without asking, then show a notice with an Undo link/button.
+				// Doing an autosave will take few seconds and may take up to 30 and fail if network connectivity is bad
+				// Restoring the post will leave the user with the proper content, but it won't be saved to the server until the next autosave.
+
+				this.restore_post_data = post_data;
+				this.undo_post_data = wp.autosave.getPostData();
+
+				/*
+				if ( $('#post_status').val() == 'publish' ) {
+					// Different message when a post is published?
+					// Comparing the current and saved post data may fail (false positive) when the post is published
+					// as in some cases there are changes to post_content on publishing and updating before saving to the DB.
+				}
+				*/
+
+				notice = $('#local-storage-notice');
+				$('form#post').before( notice.addClass('updated').show() );
+
+				notice.on( 'click', function(e) {
+					var target = $( e.target );
+
+					if ( target.hasClass('restore-backup') ) {
+						self.restorePost( self.restore_post_data );
+						target.parent().hide();
+						$(this).find('p.undo-restore').show();
+					} else if ( target.hasClass('undo-restore-backup') ) {
+						self.restorePost( self.undo_post_data );
+						target.parent().hide();
+						$(this).find('p.local-restore').show();
+					}
+
+					e.preventDefault();
+				});
+			}
+		}
+	},
+
+	// Restore the current title, content and excerpt from post_data.
+	restorePost: function( post_data ) {
+		var editor;
+
+		if ( post_data ) {
+			// Set the last saved data
+			this.lastsaveddata = post_data.post_title + ': ' + post_data.content;
+
+			if ( $('#title').val() != post_data.post_title )
+				$('#title').focus().val( post_data.post_title || '' );
+
+			$('#excerpt').val( post_data.excerpt || '' );
+			editor = typeof tinymce != 'undefined' && tinymce.get('content');
+
+			if ( editor && ! editor.isHidden() ) {
+				// Make sure there's an undo level in the editor
+				editor.undoManager.add();
+				editor.setContent( post_data.content ? switchEditors.wpautop( post_data.content ) : '' );
+			} else {
+				// Make sure the Text editor is selected
+				$('#content-html').click();
+				$('#content').val( post_data.content );
+			}
+
+			return true;
+		}
+
+		return false;
+	}
+}
+
+wp.autosave.local.init();
+
+}(jQuery));
Index: wp-includes/script-loader.php
===================================================================
--- wp-includes/script-loader.php	(revision 23658)
+++ wp-includes/script-loader.php	(working copy)
@@ -106,7 +106,7 @@
 		'dismiss' => __('Dismiss'),
 	) );
 
-	$scripts->add( 'autosave', "/wp-includes/js/autosave$suffix.js", array('schedule', 'wp-ajax-response'), false, 1 );
+	$scripts->add( 'autosave', "/wp-includes/js/autosave$suffix.js", array('schedule', 'wp-ajax-response', 'editor'), false, 1 );
 
 	$scripts->add( 'heartbeat', "/wp-includes/js/heartbeat$suffix.js", array('jquery'), false, 1 );
 	did_action( 'init' ) && $scripts->localize( 'heartbeat', 'heartbeatSettings',
@@ -587,7 +587,8 @@
 	wp_localize_script( 'autosave', 'autosaveL10n', array(
 		'autosaveInterval' => AUTOSAVE_INTERVAL,
 		'savingText' => __('Saving Draft&#8230;'),
-		'saveAlert' => __('The changes you made will be lost if you navigate away from this page.')
+		'saveAlert' => __('The changes you made will be lost if you navigate away from this page.'),
+		'blog_id' => get_current_blog_id(),
 	) );
 
 }
Index: wp-login.php
===================================================================
--- wp-login.php	(revision 23658)
+++ wp-login.php	(working copy)
@@ -68,6 +68,15 @@
 		<meta name="viewport" content="width=320; initial-scale=0.9; maximum-scale=1.0; user-scalable=0;" /><?php
 	}
 
+	// Remove all stored post data on logging out.
+	// This could be added by add_action('login_head'...) like wp_shake_js()
+	// but maybe better if it's not removable by plugins
+	if ( 'loggedout' == $wp_error->get_error_code() ) {
+		?>
+		<script>if("sessionStorage" in window){try{for(var key in sessionStorage){if(key.indexOf("wp-autosave-")!=-1){sessionStorage.removeItem(key)}}}catch(e){}};</script>
+		<?php
+	}
+
 	do_action( 'login_enqueue_scripts' );
 	do_action( 'login_head' );