--- a/browser/components/dirprovider/DirectoryProvider.cpp
+++ b/browser/components/dirprovider/DirectoryProvider.cpp
@@ -7,17 +7,16 @@
 
 #include "nsIFile.h"
 #include "nsISimpleEnumerator.h"
 #include "nsIPrefService.h"
 #include "nsIPrefBranch.h"
 
 #include "nsArrayEnumerator.h"
 #include "nsEnumeratorUtils.h"
-#include "nsBrowserDirectoryServiceDefs.h"
 #include "nsAppDirectoryServiceDefs.h"
 #include "nsDirectoryServiceDefs.h"
 #include "nsCategoryManagerUtils.h"
 #include "nsComponentManagerUtils.h"
 #include "nsCOMArray.h"
 #include "nsDirectoryServiceUtils.h"
 #include "mozilla/ModuleUtils.h"
 #include "nsServiceManagerUtils.h"
@@ -53,25 +52,16 @@ DirectoryProvider::GetFile(const char *a
     if (prefs) {
       nsCString path;
       rv = prefs->GetCharPref("browser.bookmarks.file", getter_Copies(path));
       if (NS_SUCCEEDED(rv)) {
         NS_NewNativeLocalFile(path, true, getter_AddRefs(file));
       }
     }
   }
-  else if (!strcmp(aKey, NS_APP_EXISTING_PREF_OVERRIDE)) {
-    rv = NS_GetSpecialDirectory(NS_APP_DEFAULTS_50_DIR,
-                                getter_AddRefs(file));
-    NS_ENSURE_SUCCESS(rv, rv);
-
-    file->AppendNative(NS_LITERAL_CSTRING("existing-profile-defaults.js"));
-    file.swap(*aResult);
-    return NS_OK;
-  }
   else {
     return NS_ERROR_FAILURE;
   }
 
   nsDependentCString leafstr(leafName);
 
   nsCOMPtr<nsIFile> parentDir;
   if (file) {

deleted file mode 100644
--- a/browser/components/dirprovider/nsBrowserDirectoryServiceDefs.h
+++ /dev/null
@@ -1,24 +0,0 @@
-/* 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/. */
-
-#ifndef nsBrowserDirectoryServiceDefs_h___
-#define nsBrowserDirectoryServiceDefs_h___
-
-//=============================================================================
-//
-// Defines property names for directories available from the browser-specific
-// nsBrowserDirectoryProvider.
-//
-// System and XPCOM properties are defined in nsDirectoryServiceDefs.h.
-// General application properties are defined in nsAppDirectoryServiceDefs.h.
-//
-//=============================================================================
-
-// ----------------------------------------------------------------------------
-// Files and directories that exist on a per-browser basis.
-// ----------------------------------------------------------------------------
-
-#define NS_APP_EXISTING_PREF_OVERRIDE           "ExistingPrefOverride"
-
-#endif

--- a/browser/components/dirprovider/tests/unit/test_keys.js
+++ b/browser/components/dirprovider/tests/unit/test_keys.js
@@ -5,26 +5,17 @@
 function test_bookmarkhtml() {
   let bmarks = gProfD.clone();
   bmarks.append("bookmarks.html");
 
   let tbmarks = gDirSvc.get("BMarks", Ci.nsIFile);
   do_check_true(bmarks.equals(tbmarks));
 }
 
-function test_prefoverride() {
-  let dir = gDirSvc.get("DefRt", Ci.nsIFile);
-  dir.append("existing-profile-defaults.js");
-
-  let tdir = gDirSvc.get("ExistingPrefOverride", Ci.nsIFile);
-  do_check_true(dir.equals(tdir));
-}
-
 function run_test() {
-  [test_bookmarkhtml,
-   test_prefoverride
+  [test_bookmarkhtml
   ].forEach(function(f) {
     do_test_pending();
     print("Running test: " + f.name);
     f();
     do_test_finished();
   });
 }

--- a/browser/components/nsBrowserContentHandler.js
+++ b/browser/components/nsBrowserContentHandler.js
@@ -167,50 +167,16 @@ function getPostUpdateOverridePage(defau
   // The existence of silent or the non-existence of showURL in the actions both
   // mean that an override page should not be displayed.
   if (actions.indexOf("silent") != -1 || actions.indexOf("showURL") == -1)
     return "";
 
   return update.getProperty("openURL") || defaultOverridePage;
 }
 
-// Copies a pref override file into the user's profile pref-override folder,
-// and then tells the pref service to reload its default prefs.
-function copyPrefOverride() {
-  try {
-    var fileLocator = Components.classes["@mozilla.org/file/directory_service;1"]
-                                .getService(Components.interfaces.nsIProperties);
-    const NS_APP_EXISTING_PREF_OVERRIDE = "ExistingPrefOverride";
-    var prefOverride = fileLocator.get(NS_APP_EXISTING_PREF_OVERRIDE,
-                                       Components.interfaces.nsIFile);
-    if (!prefOverride.exists())
-      return; // nothing to do
-
-    const NS_APP_PREFS_OVERRIDE_DIR     = "PrefDOverride";
-    var prefOverridesDir = fileLocator.get(NS_APP_PREFS_OVERRIDE_DIR,
-                                           Components.interfaces.nsIFile);
-
-    // Check for any existing pref overrides, and remove them if present
-    var existingPrefOverridesFile = prefOverridesDir.clone();
-    existingPrefOverridesFile.append(prefOverride.leafName);
-    if (existingPrefOverridesFile.exists())
-      existingPrefOverridesFile.remove(false);
-
-    prefOverride.copyTo(prefOverridesDir, null);
-
-    // Now that we've installed the new-profile pref override file,
-    // re-read the default prefs.
-    var prefSvcObs = Components.classes["@mozilla.org/preferences-service;1"]
-                               .getService(Components.interfaces.nsIObserver);
-    prefSvcObs.observe(null, "reload-default-prefs", null);
-  } catch (ex) {
-    Components.utils.reportError(ex);
-  }
-}
-
 // Flag used to indicate that the arguments to openWindow can be passed directly.
 const NO_EXTERNAL_URIS = 1;
 
 function openWindow(parent, url, target, features, args, noExternalArgs) {
   var wwatch = Components.classes["@mozilla.org/embedcomp/window-watcher;1"]
                          .getService(nsIWindowWatcher);
 
   if (noExternalArgs == NO_EXTERNAL_URIS) {
@@ -595,19 +561,16 @@ nsBrowserContentHandler.prototype = {
       let override = needHomepageOverride(prefb);
       if (override != OVERRIDE_NONE) {
         switch (override) {
           case OVERRIDE_NEW_PROFILE:
             // New profile.
             overridePage = Services.urlFormatter.formatURLPref("startup.homepage_welcome_url");
             break;
           case OVERRIDE_NEW_MSTONE:
-            // Existing profile, new milestone build.
-            copyPrefOverride();
-
             // Check whether we have a session to restore. If we do, we assume
             // that this is an "update" session.
             var ss = Components.classes["@mozilla.org/browser/sessionstartup;1"]
                                .getService(Components.interfaces.nsISessionStartup);
             haveUpdateSession = ss.doRestore();
             overridePage = Services.urlFormatter.formatURLPref("startup.homepage_override_url");
             if (prefb.prefHasUserValue("app.update.postupdate"))
               overridePage = getPostUpdateOverridePage(overridePage);

--- a/browser/locales/Makefile.in
+++ b/browser/locales/Makefile.in
@@ -94,27 +94,16 @@ include $(topsrcdir)/config/rules.mk
 
 include $(topsrcdir)/toolkit/locales/l10n.mk
 
 $(STAGEDIST): $(DIST)/branding
 
 $(DIST)/branding:
 	$(NSINSTALL) -D $@
 
-libs::
-	@if test -f "$(LOCALE_SRCDIR)/existing-profile-defaults.js"; then \
-	  $(PYTHON) $(topsrcdir)/config/Preprocessor.py $(PREF_PPFLAGS) $(DEFINES) $(ACDEFINES) $(XULPPFLAGS) \
-	    $(LOCALE_SRCDIR)/existing-profile-defaults.js > $(FINAL_TARGET)/defaults/existing-profile-defaults.js; \
-	fi
-install::
-	@if test -f "$(LOCALE_SRCDIR)/existing-profile-defaults.js"; then \
-	  $(PYTHON) $(topsrcdir)/config/Preprocessor.py $(PREF_PPFLAGS) $(DEFINES) $(ACDEFINES) $(XULPPFLAGS) \
-	    $(LOCALE_SRCDIR)/existing-profile-defaults.js > $(DESTDIR)$(mozappdir)/defaults/existing-profile-defaults.js; \
-	fi
-
 PROFILE_FILES = \
 	localstore.rdf \
 	mimeTypes.rdf \
 	$(NULL)
 
 PROFILE_CHROME = userChrome-example.css userContent-example.css
 
 NO_JA_JP_MAC_AB_CD := $(if $(filter ja-JP-mac, $(AB_CD)),ja,$(AB_CD))