--- a/booket.js	Tue Sep 30 21:32:39 2014 +0200
+++ b/booket.js	Thu Oct 02 09:08:22 2014 +0200
@@ -705,8 +705,11 @@
 };
 
 BookmarkModel.prototype.parseLoadedBookmarks = function (data) {
+    var wasEmpty = !this._bookmarks.size;
     var parsedData;
     var bookmarks = [];
+    var bookmark;
+    var oldBookmark;
 
     try {
         parsedData = JSON.parse(data);
@@ -724,9 +727,13 @@
     // create a temporary list of valid bookmarks
     parsedData.bookmarks.forEach(function (bookmark) {
         if (isString(bookmark.url) && bookmark.url !== '') {
-            bookmarks.push(new Bookmark(bookmark.url, bookmark.title,
-                bookmark.favicon, bookmark.tags, bookmark.ctime,
-                bookmark.mtime));
+            bookmark = new Bookmark(bookmark.url, bookmark.title,
+                bookmark.favicon, bookmark.tags, bookmark.ctime, bookmark.mtime)
+            oldBookmark = this.get(bookmark.url);
+            if (oldBookmark === undefined ||
+                    oldBookmark.mtime < bookmark.mtime) {
+                bookmarks.push(bookmark);
+            }
         }
     }, this);
 
@@ -734,10 +741,14 @@
     this.add(bookmarks.sort(function (bookmark1, bookmark2) {
         return bookmark1.ctime - bookmark2.ctime;
     }));
-    this.unsavedChanges = false;
+    if (wasEmpty) {
+        // if there were no bookmarks before there cannot be any unsaved changes
+        this.unsavedChanges = false;
+    }
 };
 
 BookmarkModel.prototype.parseImportedBookmarks = function (data) {
+    var wasEmpty = (this._bookmarks.size > 0);
     var bookmarkDoc;
     var bookmarkElements;
     var i;
@@ -748,6 +759,8 @@
     var ctime;
     var mtime;
     var bookmarks = [];
+    var bookmark;
+    var oldBookmark;
 
     bookmarkDoc = document.implementation.createHTMLDocument();
     bookmarkDoc.open();
@@ -769,7 +782,12 @@
             mtime = !isNaN(mtime =
                 parseInt(bookmarkElements[i].getAttribute('last_modified'),
                 10)) ?  mtime * 1000 : undefined;
-            bookmarks.push(new Bookmark(url, title, favicon, tags, ctime, mtime));
+            bookmark = new Bookmark(url, title, favicon, tags, ctime, mtime);
+            oldBookmark = this.get(bookmark.url);
+            if (oldBookmark === undefined ||
+                    oldBookmark.mtime < bookmark.mtime) {
+                bookmarks.push(bookmark);
+            }
         }
     }
 
@@ -777,14 +795,18 @@
     this.add(bookmarks.sort(function (bookmark1, bookmark2) {
         return bookmark1.ctime - bookmark2.ctime;
     }));
-
-    this.unsavedChanges = false;
+    if (!wasEmpty) {
+        // if there were no bookmarks before there cannot be any unsaved changes
+        this.unsavedChanges = false;
+    }
 };
 
-BookmarkModel.prototype.loadFile = function (bookmarkFile) {
-    // delete all existing bookmarks first
-    this.delete(this._bookmarks.keys());
-    this.unsavedChanges = false;
+BookmarkModel.prototype.loadFile = function (bookmarkFile, merge) {
+    if (!merge) {
+        // delete all existing bookmarks first
+        this.delete(this._bookmarks.keys());
+        this.unsavedChanges = false;
+    }
 
     this.loadFileReader = new FileReader();
     this.loadFileReader.addEventListener('error', this);
@@ -792,10 +814,12 @@
     this.loadFileReader.readAsText(bookmarkFile);
 };
 
-BookmarkModel.prototype.importFile = function (bookmarkFile) {
-    // delete all existing bookmarks first
-    this.delete(this._bookmarks.keys());
-    this.unsavedChanges = false;
+BookmarkModel.prototype.importFile = function (bookmarkFile, merge) {
+    if (!merge) {
+        // delete all existing bookmarks first
+        this.delete(this._bookmarks.keys());
+        this.unsavedChanges = false;
+    }
 
     this.importFileReader = new FileReader();
     this.importFileReader.addEventListener('error', this);
@@ -1183,13 +1207,15 @@
             e.preventDefault();
             e.target.blur();
 
-            this.notify('load-file', e.target.file.files[0]);
+            this.notify('load-file', e.target.file.files[0],
+                e.target.merge.checked);
             e.target.reset();
         } else if (e.target.id === 'import-form') {
             e.preventDefault();
             e.target.blur();
 
-            this.notify('import-file', e.target.file.files[0]);
+            this.notify('import-file', e.target.file.files[0],
+                e.target.merge.checked);
             e.target.reset();
         } else if (e.target.id === 'export-form') {
             e.preventDefault();
@@ -1731,7 +1757,7 @@
     history.pushState(null, null, serializeHash(url, hashData));
 };
 
-BooketController.prototype.onLoadFile = function (bookmarkFile) {
+BooketController.prototype.onLoadFile = function (bookmarkFile, merge) {
     if (this.bookmarkModel.unsavedChanges) {
         if (!this.actionsView.confirmLoadFile()) {
             return;
@@ -1739,10 +1765,10 @@
         this.bookmarkModel.unsavedChanges = false;
     }
 
-    this.bookmarkModel.loadFile(bookmarkFile);
+    this.bookmarkModel.loadFile(bookmarkFile, merge);
 };
 
-BooketController.prototype.onImportFile = function (bookmarkFile) {
+BooketController.prototype.onImportFile = function (bookmarkFile, merge) {
     if (this.bookmarkModel.unsavedChanges) {
         if (!this.actionsView.confirmLoadFile()) {
             return;
@@ -1750,7 +1776,7 @@
         this.bookmarkModel.unsavedChanges = false;
     }
 
-    this.bookmarkModel.importFile(bookmarkFile);
+    this.bookmarkModel.importFile(bookmarkFile, merge);
 };
 
 BooketController.prototype.onEditBookmark = function (bookmarkUrl) {