--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -626,16 +626,19 @@ pref("browser.preferences.instantApply",
 pref("browser.preferences.instantApply", true);
 #endif
 #ifdef XP_MACOSX
 pref("browser.preferences.animateFadeIn", true);
 #else
 pref("browser.preferences.animateFadeIn", false);
 #endif
 
+// Toggles between the two Preferences implementations, pop-up window and in-content
+pref("browser.preferences.inContent", false);
+
 pref("browser.download.show_plugins_in_list", true);
 pref("browser.download.hide_plugins_without_extensions", true);
 
 // Backspace and Shift+Backspace behavior
 // 0 goes Back/Forward
 // 1 act like PgUp/PgDown
 // 2 and other values, nothing
 #ifdef UNIX_BUT_NOT_MAC

--- a/browser/base/content/test/Makefile.in
+++ b/browser/base/content/test/Makefile.in
@@ -176,16 +176,17 @@ endif
                  browser_bug623155.js \
                  browser_bug623893.js \
                  browser_bug624734.js \
                  browser_bug647886.js \
                  browser_bug655584.js \
                  browser_bug664672.js \
                  browser_bug710878.js \
                  browser_bug719271.js \
+                 browser_bug735471.js \
                  browser_bug743421.js \
                  browser_bug749738.js \
                  browser_canonizeURL.js \
                  browser_findbarClose.js \
                  browser_homeDrop.js \
                  browser_keywordBookmarklets.js \
                  browser_contextSearchTabPosition.js \
                  browser_ctrlTab.js \

new file mode 100644
--- /dev/null
+++ b/browser/base/content/test/browser_bug735471.js
@@ -0,0 +1,59 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public License,
+ * v. 2.0. If a copy of the MPL was not distributed with this file, You can
+ * obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+
+function test() {
+  waitForExplicitFinish();
+  registerCleanupFunction(function() {
+    // Reset pref to its default
+    Services.prefs.clearUserPref("browser.preferences.inContent");
+  });
+  
+  // Verify that about:preferences tab is displayed when
+  // browser.preferences.inContent is set to true
+  Services.prefs.setBoolPref("browser.preferences.inContent", true);
+    
+  gBrowser.tabContainer.addEventListener("TabOpen", function(aEvent) {
+    
+    gBrowser.tabContainer.removeEventListener("TabOpen", arguments.callee, true);
+    let browser = aEvent.originalTarget.linkedBrowser;
+    browser.addEventListener("load", function(aEvent) {
+      browser.removeEventListener("load", arguments.callee, true);
+      
+      is(Services.prefs.getBoolPref("browser.preferences.inContent"), true, "In-content prefs are enabled");
+      is(browser.contentWindow.location.href, "about:preferences", "Checking if the preferences tab was opened");
+      
+      gBrowser.removeCurrentTab();
+      Services.prefs.setBoolPref("browser.preferences.inContent", false);
+      openPreferences();
+      
+    }, true);
+  }, true);
+  
+  
+  let observer = {
+    observe: function(aSubject, aTopic, aData) {
+      if (aTopic == "domwindowopened") {
+        windowWatcher.unregisterNotification(observer);
+        
+        let win = aSubject.QueryInterface(Components.interfaces.nsIDOMWindow);
+        win.addEventListener("load", function() {
+          win.removeEventListener("load", arguments.callee, false);
+          is(Services.prefs.getBoolPref("browser.preferences.inContent"), false, "In-content prefs are disabled");
+          is(win.location.href, "chrome://browser/content/preferences/preferences.xul", "Checking if the preferences window was opened");
+          win.close();
+          finish();
+        }, false);
+      }
+    }
+  }
+  
+  var windowWatcher = Components.classes["@mozilla.org/embedcomp/window-watcher;1"]
+                        .getService(Components.interfaces.nsIWindowWatcher);
+  windowWatcher.registerNotification(observer);
+  
+  openPreferences();
+}

--- a/browser/base/content/utilityOverlay.js
+++ b/browser/base/content/utilityOverlay.js
@@ -490,37 +490,41 @@ function openAboutDialog() {
 #else
   var features = "chrome,centerscreen,dependent,dialog=no";
 #endif
   window.openDialog("chrome://browser/content/aboutDialog.xul", "", features);
 }
 
 function openPreferences(paneID, extraArgs)
 {
-  var instantApply = getBoolPref("browser.preferences.instantApply", false);
-  var features = "chrome,titlebar,toolbar,centerscreen" + (instantApply ? ",dialog=no" : ",modal");
+  if (Services.prefs.getBoolPref("browser.preferences.inContent")) {  
+    openUILinkIn("about:preferences", "tab");
+  } else {
+    var instantApply = getBoolPref("browser.preferences.instantApply", false);
+    var features = "chrome,titlebar,toolbar,centerscreen" + (instantApply ? ",dialog=no" : ",modal");
 
-  var win = Services.wm.getMostRecentWindow("Browser:Preferences");
-  if (win) {
-    win.focus();
-    if (paneID) {
-      var pane = win.document.getElementById(paneID);
-      win.document.documentElement.showPane(pane);
+    var win = Services.wm.getMostRecentWindow("Browser:Preferences");
+    if (win) {
+      win.focus();
+      if (paneID) {
+        var pane = win.document.getElementById(paneID);
+        win.document.documentElement.showPane(pane);
+      }
+
+      if (extraArgs && extraArgs["advancedTab"]) {
+        var advancedPaneTabs = win.document.getElementById("advancedPrefs");
+        advancedPaneTabs.selectedTab = win.document.getElementById(extraArgs["advancedTab"]);
+      }
+
+     return win;
     }
 
-    if (extraArgs && extraArgs["advancedTab"]) {
-      var advancedPaneTabs = win.document.getElementById("advancedPrefs");
-      advancedPaneTabs.selectedTab = win.document.getElementById(extraArgs["advancedTab"]);
-    }
-
-    return win;
+    return openDialog("chrome://browser/content/preferences/preferences.xul",
+                      "Preferences", features, paneID, extraArgs);
   }
-
-  return openDialog("chrome://browser/content/preferences/preferences.xul",
-                    "Preferences", features, paneID, extraArgs);
 }
 
 function openAdvancedPreferences(tabID)
 {
   return openPreferences("paneAdvanced", { "advancedTab" : tabID });
 }
 
 /**

--- a/browser/components/nsBrowserContentHandler.js
+++ b/browser/components/nsBrowserContentHandler.js
@@ -285,24 +285,43 @@ function openWindow(parent, url, target,
   argArray.AppendElement(null); // referer
   argArray.AppendElement(null); // postData
   argArray.AppendElement(null); // allowThirdPartyFixup
 
   return wwatch.openWindow(parent, url, target, features, argArray);
 }
 
 function openPreferences() {
-  var features = "chrome,titlebar,toolbar,centerscreen,dialog=no";
-  var url = "chrome://browser/content/preferences/preferences.xul";
+  if (Services.prefs.getBoolPref("browser.preferences.inContent")) { 
+    var sa = Components.classes["@mozilla.org/supports-array;1"]
+                       .createInstance(Components.interfaces.nsISupportsArray);
+
+    var wuri = Components.classes["@mozilla.org/supports-string;1"]
+                         .createInstance(Components.interfaces.nsISupportsString);
+    wuri.data = "about:preferences";
+
+    sa.AppendElement(wuri);
+
+    var wwatch = Components.classes["@mozilla.org/embedcomp/window-watcher;1"]
+                           .getService(nsIWindowWatcher);
 
-  var win = getMostRecentWindow("Browser:Preferences");
-  if (win) {
-    win.focus();
+    wwatch.openWindow(null, gBrowserContentHandler.chromeURL,
+                      "_blank",
+                      "chrome,dialog=no,all",
+                      sa);
   } else {
-    openWindow(null, url, "_blank", features);
+    var features = "chrome,titlebar,toolbar,centerscreen,dialog=no";
+    var url = "chrome://browser/content/preferences/preferences.xul";
+    
+    var win = getMostRecentWindow("Browser:Preferences");
+    if (win) {
+      win.focus();
+    } else {
+      openWindow(null, url, "_blank", features);
+    }
   }
 }
 
 function getMostRecentWindow(aType) {
   var wm = Components.classes["@mozilla.org/appshell/window-mediator;1"]
                      .getService(nsIWindowMediator);
   return wm.getMostRecentWindow(aType);
 }