--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -158,17 +158,17 @@ pref("app.update.url", "https://aus5.moz
 // app.update.interval is in branding section
 // app.update.promptWaitTime is in branding section
 
 // Whether or not to attempt using the service for updates.
 #ifdef MOZ_MAINTENANCE_SERVICE
   pref("app.update.service.enabled", true);
 #endif
 
-#ifdef XP_WIN
+#ifdef MOZ_BITS_DOWNLOAD
   // If set to true, the Update Service will attempt to use Windows BITS to
   // download updates and will fallback to downloading internally if that fails.
   pref("app.update.BITS.enabled", true);
 #endif
 
 // Symmetric (can be overridden by individual extensions) update preferences.
 // e.g.
 //  extensions.{GUID}.update.enabled

--- a/toolkit/components/bitsdownload/Bits.jsm
+++ b/toolkit/components/bitsdownload/Bits.jsm
@@ -22,17 +22,17 @@ const { AppConstants } = ChromeUtils.imp
 const { XPCOMUtils } = ChromeUtils.import(
   "resource://gre/modules/XPCOMUtils.jsm"
 );
 
 // This conditional prevents errors if this file is imported from operating
 // systems other than Windows. This is purely for convenient importing, because
 // attempting to use anything in this file on platforms other than Windows will
 // result in an error.
-if (AppConstants.platform == "win") {
+if (AppConstants.MOZ_BITS_DOWNLOAD) {
   XPCOMUtils.defineLazyServiceGetter(
     this,
     "gBits",
     "@mozilla.org/bits;1",
     "nsIBits"
   );
 }
 

--- a/toolkit/components/bitsdownload/components.conf
+++ b/toolkit/components/bitsdownload/components.conf
@@ -1,16 +1,16 @@
 # -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
 # vim: set filetype=python:
 # 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/.
 
 Classes = []
-if buildconfig.substs['OS_ARCH'] == 'WINNT' and defined('MOZ_BITS_DOWNLOAD'):
+if defined('MOZ_BITS_DOWNLOAD'):
     Classes += [
         {
             'cid': '{495d6f3d-9748-4d30-8ce5-0290c0001edf}',
             'contract_ids': ['@mozilla.org/bits;1'],
             'singleton': True,
             'constructor': 'GetBitsService',
             'headers': ['Bits.h'],
         },

--- a/toolkit/components/bitsdownload/moz.build
+++ b/toolkit/components/bitsdownload/moz.build
@@ -9,17 +9,17 @@ XPIDL_MODULE = 'Bits'
 XPIDL_SOURCES += [
     'nsIBits.idl',
 ]
 
 XPCOM_MANIFESTS += [
     'components.conf',
 ]
 
-if CONFIG['OS_ARCH'] == 'WINNT':
+if CONFIG['MOZ_BITS_DOWNLOAD']:
   EXPORTS += [
     'Bits.h'
   ]
   UNIFIED_SOURCES += [
     'Bits.cpp'
   ]
 
 EXTRA_JS_MODULES += [

--- a/toolkit/mozapps/update/tests/moz.build
+++ b/toolkit/mozapps/update/tests/moz.build
@@ -5,17 +5,17 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 HAS_MISC_RULE = True
 
 FINAL_TARGET = '_tests/xpcshell/toolkit/mozapps/update/tests/data'
 
 if not CONFIG['MOZ_SUITE']:
     BROWSER_CHROME_MANIFESTS += ['browser/browser.ini']
-    if CONFIG['OS_ARCH'] == 'WINNT':
+    if CONFIG['MOZ_BITS_DOWNLOAD']:
         BROWSER_CHROME_MANIFESTS += ['browser/browser.bits.ini']
 
 XPCSHELL_TESTS_MANIFESTS += [
     'unit_aus_update/xpcshell.ini',
     'unit_base_updater/xpcshell.ini'
 ]
 
 if CONFIG['MOZ_MAINTENANCE_SERVICE']: