--- a/dom/base/Document.cpp
+++ b/dom/base/Document.cpp
@@ -90,16 +90,17 @@
 #include "PermissionDelegateHandler.h"
 
 #include "mozilla/AsyncEventDispatcher.h"
 #include "mozilla/BasicEvents.h"
 #include "mozilla/EventListenerManager.h"
 #include "mozilla/EventStateManager.h"
 #include "mozilla/FullscreenChange.h"
 #include "mozilla/PendingAnimationTracker.h"
+#include "mozilla/intl/LocaleService.h"
 
 #include "mozilla/dom/Attr.h"
 #include "mozilla/dom/BindingDeclarations.h"
 #include "mozilla/dom/BrowsingContext.h"
 #include "mozilla/dom/ContentChild.h"
 #include "mozilla/dom/CSSImportRule.h"
 #include "mozilla/dom/CSPDictionariesBinding.h"
 #include "mozilla/dom/DOMIntersectionObserver.h"
@@ -306,17 +307,16 @@
 #include "mozilla/dom/SVGSVGElement.h"
 #include "mozilla/dom/DocGroup.h"
 #include "mozilla/dom/TabGroup.h"
 #include "mozilla/dom/ChromeObserver.h"
 #ifdef MOZ_XUL
 #  include "mozilla/dom/XULBroadcastManager.h"
 #  include "mozilla/dom/XULPersist.h"
 #  include "nsIAppWindow.h"
-#  include "nsIChromeRegistry.h"
 #  include "nsXULPrototypeDocument.h"
 #  include "nsXULCommandDispatcher.h"
 #  include "nsXULPopupManager.h"
 #  include "nsIDocShellTreeOwner.h"
 #endif
 
 #include "mozilla/DocLoadingTimelineMarker.h"
 
@@ -11568,38 +11568,22 @@ bool Document::IsDocumentRightToLeft() {
         return false;
       case 1:
         return true;
       default:
         break;  // otherwise, not a valid value, so fall through
     }
   }
 
-  // otherwise, get the locale from the chrome registry and
-  // look up the intl.uidirection.<locale> preference
-  nsCOMPtr<nsIXULChromeRegistry> reg =
-      mozilla::services::GetXULChromeRegistryService();
-  if (!reg) return false;
-
-  nsAutoCString package;
-  if (mDocumentURI->SchemeIs("chrome")) {
-    mDocumentURI->GetHostPort(package);
-  } else {
-    // use the 'global' package for about and resource uris.
-    // otherwise, just default to left-to-right.
-    if (mDocumentURI->SchemeIs("about") || mDocumentURI->SchemeIs("resource")) {
-      package.AssignLiteral("global");
-    } else {
-      return false;
-    }
-  }
-
-  bool isRTL = false;
-  reg->IsLocaleRTL(package, &isRTL);
-  return isRTL;
+  if (!mDocumentURI->SchemeIs("chrome") && !mDocumentURI->SchemeIs("about") &&
+      !mDocumentURI->SchemeIs("resource")) {
+    return false;
+  }
+
+  return intl::LocaleService::GetInstance()->IsAppLocaleRTL();
 }
 
 class nsDelayedEventDispatcher : public Runnable {
  public:
   explicit nsDelayedEventDispatcher(nsTArray<nsCOMPtr<Document>>& aDocuments)
       : mozilla::Runnable("nsDelayedEventDispatcher") {
     mDocuments.SwapElements(aDocuments);
   }

--- a/toolkit/content/tests/chrome/chrome.ini
+++ b/toolkit/content/tests/chrome/chrome.ini
@@ -47,18 +47,16 @@ support-files =
   window_showcaret.xhtml
   window_subframe_origin.xhtml
   window_titlebar.xhtml
   window_tooltip.xhtml
   xul_selectcontrol.js
   rtlchrome/rtl.css
   rtlchrome/rtl.dtd
   rtlchrome/rtl.manifest
-  rtltest/righttoleft.manifest
-  rtltest/content/dirtest.xhtml
 
 [test_about_networking.html]
 [test_arrowpanel.xhtml]
 skip-if = (verify && (os == 'win')) || (debug && (os == 'win') && (bits == 32)) # Bug 1546256
 [test_autocomplete2.xhtml]
 [test_autocomplete3.xhtml]
 [test_autocomplete4.xhtml]
 [test_autocomplete5.xhtml]
@@ -164,17 +162,16 @@ skip-if = (verify && (os == 'win'))
 [test_preferences.xhtml]
 [test_preferences_beforeaccept.xhtml]
 support-files = window_preferences_beforeaccept.xhtml
 [test_preferences_onsyncfrompreference.xhtml]
 support-files = window_preferences_onsyncfrompreference.xhtml
 [test_props.xhtml]
 [test_radio.xhtml]
 [test_richlistbox.xhtml]
-[test_righttoleft.xhtml]
 [test_screenPersistence.xhtml]
 [test_scrollbar.xhtml]
 [test_showcaret.xhtml]
 [test_subframe_origin.xhtml]
 [test_tabbox.xhtml]
 [test_tabindex.xhtml]
 [test_textbox_search.xhtml]
 [test_titlebar.xhtml]

deleted file mode 100644
--- a/toolkit/content/tests/chrome/rtltest/content/dirtest.xhtml
+++ /dev/null
@@ -1,25 +0,0 @@
-<?xml version="1.0"?>
-
-<?xml-stylesheet href="chrome://global/skin" type="text/css"?>
-
-<window xmlns:html="http://www.w3.org/1999/xhtml"
-        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
-
-<html:style>
-hbox, vbox { background-color: white; }
-hbox:-moz-locale-dir(ltr) { background-color: yellow; }
-vbox:-moz-locale-dir(rtl) { background-color: green; }
-</html:style>
-
-<hbox id="hbox">
-  <button label="One"/>
-  <button label="Two"/>
-  <button label="Three"/>
-</hbox>
-<vbox id="vbox">
-  <button label="One"/>
-  <button label="Two"/>
-  <button label="Three"/>
-</vbox>
-
-</window>

deleted file mode 100644
--- a/toolkit/content/tests/chrome/rtltest/righttoleft.manifest
+++ /dev/null
@@ -1,3 +0,0 @@
-content ltrtest content/
-content rtltest content/
-locale rtltest ar-QA content/

deleted file mode 100644
--- a/toolkit/content/tests/chrome/test_righttoleft.xhtml
+++ /dev/null
@@ -1,120 +0,0 @@
-<?xml version="1.0"?>
-<?xml-stylesheet href="chrome://global/skin" type="text/css"?>
-<?xml-stylesheet 
-  href="chrome://mochikit/content/tests/SimpleTest/test.css"
-  type="text/css"?>
-
-<window title="Right to Left UI Test"
-        onload="runTest()"
-        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
-
-  <script type="application/javascript" 
-          src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
-  <script type="application/javascript" 
-          src="chrome://mochikit/content/chrome-harness.js"></script>
-  <script type="application/javascript" 
-          src="RegisterUnregisterChrome.js"></script>
-
-  <body  xmlns="http://www.w3.org/1999/xhtml">
-    <p id="display"></p>
-    <div id="content" style="display: none">
-    </div>
-    <pre id="test">
-    </pre>
-  </body>
-
-  <iframe id="subframe" width="100" height="100" onload="frameLoaded();"/>
-
-  <script type="application/javascript">
-    <![CDATA[
-
-      SimpleTest.waitForExplicitFinish();
-
-      let prefs = Cc["@mozilla.org/preferences-service;1"].
-                  getService(Ci.nsIPrefBranch);
-      const UI_DIRECTION_PREF = "intl.uidirection";
-      prefs.setIntPref(UI_DIRECTION_PREF, -1);
-
-      let rootDir = getRootDirectory(window.location.href);
-      registerManifestPermanently(rootDir + "rtltest/righttoleft.manifest");
-
-      function runTest()
-      {
-        var subframe = document.getElementById("subframe");
-        subframe.setAttribute("src", "chrome://ltrtest/content/dirtest.xhtml");
-      }
-
-      function frameLoaded()
-      {
-        var subframe = document.getElementById("subframe");
-        var subwin = subframe.contentWindow;
-        var subdoc = subframe.contentDocument;
-        var url = String(subwin.location);
-        if (url.indexOf("chrome://ltrtest") == 0) {
-          is(subwin.getComputedStyle(subdoc.getElementById("hbox")).backgroundColor,
-             "rgb(255, 255, 0)", "left to right with :-moz-locale-dir(ltr)");
-          is(subwin.getComputedStyle(subdoc.getElementById("vbox")).backgroundColor,
-             "rgb(255, 255, 255)", "left to right with :-moz-locale-dir(rtl)");
-
-          is(subwin.getComputedStyle(subdoc.documentElement).direction, "ltr",
-             "left to right direction");
-
-          subdoc.documentElement.setAttribute("localedir", "rtl");
-
-          is(subwin.getComputedStyle(subdoc.getElementById("hbox")).backgroundColor,
-             "rgb(255, 255, 255)", "left to right with :-moz-locale-dir(ltr) and localedir='rtl'");
-          is(subwin.getComputedStyle(subdoc.getElementById("vbox")).backgroundColor,
-             "rgb(0, 128, 0)", "left to right with :-moz-locale-dir(rtl) and localedir='rtl'");
-          is(subwin.getComputedStyle(subdoc.documentElement).direction, "rtl",
-             "left to right direction with localedir='rtl'");
-
-          subdoc.documentElement.removeAttribute("localedir");
-
-          is(subwin.getComputedStyle(subdoc.getElementById("hbox")).backgroundColor,
-             "rgb(255, 255, 0)", "left to right with :-moz-locale-dir(ltr) and localedir removed");
-          is(subwin.getComputedStyle(subdoc.getElementById("vbox")).backgroundColor,
-             "rgb(255, 255, 255)", "left to right with :-moz-locale-dir(rtl) and localedir removed");
-          is(subwin.getComputedStyle(subdoc.documentElement).direction, "ltr",
-             "left to right direction with localedir removed");
-
-          subframe.setAttribute("src", "chrome://rtltest/content/dirtest.xhtml");
-        }
-        else if (url.indexOf("chrome://rtltest") == 0) {
-          is(subwin.getComputedStyle(subdoc.getElementById("hbox")).backgroundColor,
-             "rgb(255, 255, 255)", "right to left with :-moz-locale-dir(ltr)");
-          is(subwin.getComputedStyle(subdoc.getElementById("vbox")).backgroundColor,
-             "rgb(0, 128, 0)", "right to left with :-moz-locale-dir(rtl)");
-          is(subwin.getComputedStyle(subdoc.documentElement).direction, "rtl",
-             "right to left direction");
-
-          subdoc.documentElement.setAttribute("localedir", "ltr");
-
-          is(subwin.getComputedStyle(subdoc.getElementById("hbox")).backgroundColor,
-             "rgb(255, 255, 0)", "right to left with :-moz-locale-dir(ltr) and localedir='ltr'");
-          is(subwin.getComputedStyle(subdoc.getElementById("vbox")).backgroundColor,
-             "rgb(255, 255, 255)", "right to left with :-moz-locale-dir(rtl) and localedir='ltr'");
-          is(subwin.getComputedStyle(subdoc.documentElement).direction, "ltr",
-             "right to left direction with localedir='ltr'");
-
-          subdoc.documentElement.removeAttribute("localedir");
-
-          prefs.setIntPref(UI_DIRECTION_PREF, -1);
-          is(subwin.getComputedStyle(subdoc.documentElement).direction, "rtl",
-             "right to left direction with default uidirection preference");
-          prefs.setIntPref(UI_DIRECTION_PREF, 0);
-          is(subwin.getComputedStyle(subdoc.documentElement).direction, "ltr",
-             "right to left direction overridden by uidirection preference = 0");
-          prefs.setIntPref(UI_DIRECTION_PREF, 1);
-          is(subwin.getComputedStyle(subdoc.documentElement).direction, "rtl",
-             "right to left direction overridden by uidirection preference = 1");
-
-          if (prefs.prefHasUserValue(UI_DIRECTION_PREF))
-            prefs.clearUserPref(UI_DIRECTION_PREF);
-
-          SimpleTest.finish();
-        }
-      }
-    ]]>
-  </script>
-
-</window>