diff --git a/accessible/generic/Accessible.cpp b/accessible/generic/Accessible.cpp
index f10aee1e3900..2e98004304e7 100644
--- a/accessible/generic/Accessible.cpp
+++ b/accessible/generic/Accessible.cpp
@@ -57,7 +57,7 @@
 #include "nsIScrollableFrame.h"
 #include "nsFocusManager.h"
 
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsUnicharUtils.h"
 #include "nsReadableUtils.h"
 #include "prdtoa.h"
diff --git a/caps/SystemPrincipal.cpp b/caps/SystemPrincipal.cpp
index cf9d0deb42c1..47e81afb7522 100644
--- a/caps/SystemPrincipal.cpp
+++ b/caps/SystemPrincipal.cpp
@@ -11,7 +11,6 @@
 #include "nsIServiceManager.h"
 #include "nsIURL.h"
 #include "nsCOMPtr.h"
-#include "nsXPIDLString.h"
 #include "nsReadableUtils.h"
 #include "nsCRT.h"
 #include "nsString.h"
diff --git a/caps/nsJSPrincipals.cpp b/caps/nsJSPrincipals.cpp
index 6a69d5b12b60..d9b16d6b56b4 100644
--- a/caps/nsJSPrincipals.cpp
+++ b/caps/nsJSPrincipals.cpp
@@ -9,7 +9,6 @@
 #include "nsIObjectInputStream.h"
 #include "nsJSPrincipals.h"
 #include "plstr.h"
-#include "nsXPIDLString.h"
 #include "nsCOMPtr.h"
 #include "nsIServiceManager.h"
 #include "nsMemory.h"
diff --git a/caps/nsScriptSecurityManager.cpp b/caps/nsScriptSecurityManager.cpp
index f04bf9fc0ed2..5dcb7f7ec424 100644
--- a/caps/nsScriptSecurityManager.cpp
+++ b/caps/nsScriptSecurityManager.cpp
@@ -23,7 +23,7 @@
 #include "SystemPrincipal.h"
 #include "NullPrincipal.h"
 #include "DomainPolicy.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsCRT.h"
 #include "nsCRTGlue.h"
 #include "nsDocShell.h"
diff --git a/docshell/base/nsDocShellTreeOwner.cpp b/docshell/base/nsDocShellTreeOwner.cpp
index 51a5fe5e6877..e1fb8b5fac72 100644
--- a/docshell/base/nsDocShellTreeOwner.cpp
+++ b/docshell/base/nsDocShellTreeOwner.cpp
@@ -15,7 +15,7 @@
 #include "mozilla/ReflowInput.h"
 #include "nsIServiceManager.h"
 #include "nsComponentManagerUtils.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsIAtom.h"
 #include "nsReadableUtils.h"
 #include "nsUnicharUtils.h"
diff --git a/dom/base/nsHTMLContentSerializer.cpp b/dom/base/nsHTMLContentSerializer.cpp
index 64eedf723c1b..749ed6013ae9 100644
--- a/dom/base/nsHTMLContentSerializer.cpp
+++ b/dom/base/nsHTMLContentSerializer.cpp
@@ -18,7 +18,6 @@
 #include "nsNameSpaceManager.h"
 #include "nsString.h"
 #include "nsUnicharUtils.h"
-#include "nsXPIDLString.h"
 #include "nsIServiceManager.h"
 #include "nsIDocumentEncoder.h"
 #include "nsGkAtoms.h"
diff --git a/dom/base/nsScriptNameSpaceManager.cpp b/dom/base/nsScriptNameSpaceManager.cpp
index 63d65058c470..8ae6c9a7a589 100644
--- a/dom/base/nsScriptNameSpaceManager.cpp
+++ b/dom/base/nsScriptNameSpaceManager.cpp
@@ -17,7 +17,7 @@
 #include "nsIInterfaceInfoManager.h"
 #include "nsIInterfaceInfo.h"
 #include "xptinfo.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsHashKeys.h"
 #include "nsDOMClassInfo.h"
diff --git a/dom/base/nsXHTMLContentSerializer.cpp b/dom/base/nsXHTMLContentSerializer.cpp
index 4492f1776209..ac2a2ea7ba69 100644
--- a/dom/base/nsXHTMLContentSerializer.cpp
+++ b/dom/base/nsXHTMLContentSerializer.cpp
@@ -18,7 +18,6 @@
 #include "nsNameSpaceManager.h"
 #include "nsString.h"
 #include "nsUnicharUtils.h"
-#include "nsXPIDLString.h"
 #include "nsIServiceManager.h"
 #include "nsIDocumentEncoder.h"
 #include "nsGkAtoms.h"
diff --git a/dom/html/nsHTMLDocument.cpp b/dom/html/nsHTMLDocument.cpp
index 2f2e68c344cd..fa3d614854d9 100644
--- a/dom/html/nsHTMLDocument.cpp
+++ b/dom/html/nsHTMLDocument.cpp
@@ -11,7 +11,7 @@
 #include "mozilla/dom/HTMLAllCollection.h"
 #include "nsCOMPtr.h"
 #include "nsGlobalWindow.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsPrintfCString.h"
 #include "nsReadableUtils.h"
 #include "nsUnicharUtils.h"
diff --git a/dom/jsurl/nsJSProtocolHandler.cpp b/dom/jsurl/nsJSProtocolHandler.cpp
index 36f2143cab8b..f291f4ef6736 100644
--- a/dom/jsurl/nsJSProtocolHandler.cpp
+++ b/dom/jsurl/nsJSProtocolHandler.cpp
@@ -9,7 +9,7 @@
 #include "jswrapper.h"
 #include "nsCRT.h"
 #include "nsError.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsJSProtocolHandler.h"
 #include "nsStringStream.h"
@@ -28,7 +28,6 @@
 #include "nsIWindowMediator.h"
 #include "nsPIDOMWindow.h"
 #include "nsIConsoleService.h"
-#include "nsXPIDLString.h"
 #include "nsEscape.h"
 #include "nsIWebNavigation.h"
 #include "nsIDocShell.h"
diff --git a/dom/xbl/nsBindingManager.cpp b/dom/xbl/nsBindingManager.cpp
index e1228dfa20fa..f13b9f1568ca 100644
--- a/dom/xbl/nsBindingManager.cpp
+++ b/dom/xbl/nsBindingManager.cpp
@@ -13,7 +13,7 @@
 #include "nsIURI.h"
 #include "nsIURL.h"
 #include "nsIChannel.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "plstr.h"
 #include "nsIContent.h"
 #include "nsIDOMElement.h"
diff --git a/dom/xbl/nsXBLBinding.cpp b/dom/xbl/nsXBLBinding.cpp
index 26953d4e008b..9b0fccd5fe1a 100644
--- a/dom/xbl/nsXBLBinding.cpp
+++ b/dom/xbl/nsXBLBinding.cpp
@@ -12,7 +12,7 @@
 #include "nsIURI.h"
 #include "nsIURL.h"
 #include "nsIChannel.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "plstr.h"
 #include "nsIContent.h"
diff --git a/dom/xbl/nsXBLPrototypeBinding.cpp b/dom/xbl/nsXBLPrototypeBinding.cpp
index 6f23bcddaf70..e007cefb57b8 100644
--- a/dom/xbl/nsXBLPrototypeBinding.cpp
+++ b/dom/xbl/nsXBLPrototypeBinding.cpp
@@ -13,7 +13,7 @@
 #include "nsIURI.h"
 #include "nsIURL.h"
 #include "nsIChannel.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsNetUtil.h"
 #include "plstr.h"
diff --git a/dom/xbl/nsXBLPrototypeHandler.cpp b/dom/xbl/nsXBLPrototypeHandler.cpp
index 968089af3abd..51b30b428a34 100644
--- a/dom/xbl/nsXBLPrototypeHandler.cpp
+++ b/dom/xbl/nsXBLPrototypeHandler.cpp
@@ -33,7 +33,7 @@
 #include "nsIDOMWindow.h"
 #include "nsIServiceManager.h"
 #include "nsIScriptError.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsGkAtoms.h"
 #include "nsIXPConnect.h"
diff --git a/dom/xbl/nsXBLService.cpp b/dom/xbl/nsXBLService.cpp
index 0200fd144ae2..de132dc18ec6 100644
--- a/dom/xbl/nsXBLService.cpp
+++ b/dom/xbl/nsXBLService.cpp
@@ -16,7 +16,7 @@
 #include "nsIDOMElement.h"
 #include "nsIURL.h"
 #include "nsIChannel.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "plstr.h"
 #include "nsIContent.h"
 #include "nsIDocument.h"
diff --git a/dom/xml/XMLDocument.cpp b/dom/xml/XMLDocument.cpp
index 496ea9fb9523..b7d1d0250764 100644
--- a/dom/xml/XMLDocument.cpp
+++ b/dom/xml/XMLDocument.cpp
@@ -21,7 +21,7 @@
 #include "nsIDOMWindow.h"
 #include "nsIDOMDocumentType.h"
 #include "nsCOMPtr.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsIHttpChannelInternal.h"
 #include "nsIURI.h"
 #include "nsIServiceManager.h"
diff --git a/dom/xul/XULDocument.cpp b/dom/xul/XULDocument.cpp
index 875a02b98d6d..6f9270cfd647 100644
--- a/dom/xul/XULDocument.cpp
+++ b/dom/xul/XULDocument.cpp
@@ -45,7 +45,7 @@
 #include "nsParserCIID.h"
 #include "nsPIBoxObject.h"
 #include "mozilla/dom/BoxObject.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsPIDOMWindow.h"
 #include "nsPIWindowRoot.h"
 #include "nsXULCommandDispatcher.h"
diff --git a/dom/xul/nsXULContentSink.cpp b/dom/xul/nsXULContentSink.cpp
index 1cbe4d5ada31..e65f7ff546e7 100644
--- a/dom/xul/nsXULContentSink.cpp
+++ b/dom/xul/nsXULContentSink.cpp
@@ -38,7 +38,7 @@
 #include "nsLayoutCID.h"
 #include "nsNetUtil.h"
 #include "nsRDFCID.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsXULElement.h"
 #include "mozilla/Logging.h"
diff --git a/dom/xul/nsXULElement.cpp b/dom/xul/nsXULElement.cpp
index de200f7b22be..f1a87e917182 100644
--- a/dom/xul/nsXULElement.cpp
+++ b/dom/xul/nsXULElement.cpp
@@ -51,7 +51,7 @@
 #include "mozilla/dom/Event.h"
 #include "nsRDFCID.h"
 #include "nsStyleConsts.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsXULControllers.h"
 #include "nsIBoxObject.h"
 #include "nsPIBoxObject.h"
diff --git a/dom/xul/templates/nsXULContentBuilder.cpp b/dom/xul/templates/nsXULContentBuilder.cpp
index 31608ab18497..8cd9321043b4 100644
--- a/dom/xul/templates/nsXULContentBuilder.cpp
+++ b/dom/xul/templates/nsXULContentBuilder.cpp
@@ -20,7 +20,7 @@
 #include "nsTemplateRule.h"
 #include "nsTemplateMap.h"
 #include "nsTArray.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsGkAtoms.h"
 #include "nsXULContentUtils.h"
 #include "nsXULElement.h"
diff --git a/dom/xul/templates/nsXULContentUtils.cpp b/dom/xul/templates/nsXULContentUtils.cpp
index 929255ea1626..e0fc7929f067 100644
--- a/dom/xul/templates/nsXULContentUtils.cpp
+++ b/dom/xul/templates/nsXULContentUtils.cpp
@@ -29,7 +29,6 @@
 #include "nsNameSpaceManager.h"
 #include "nsRDFCID.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "nsGkAtoms.h"
 #include "mozilla/Logging.h"
 #include "prtime.h"
diff --git a/dom/xul/templates/nsXULTemplateBuilder.cpp b/dom/xul/templates/nsXULTemplateBuilder.cpp
index ff033661c021..bf72f07d5f86 100644
--- a/dom/xul/templates/nsXULTemplateBuilder.cpp
+++ b/dom/xul/templates/nsXULTemplateBuilder.cpp
@@ -54,7 +54,7 @@
 #include "nsTArray.h"
 #include "nsTemplateMatch.h"
 #include "nsTemplateRule.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsWhitespaceTokenizer.h"
 #include "nsGkAtoms.h"
 #include "nsXULElement.h"
diff --git a/extensions/cookie/nsCookieModule.cpp b/extensions/cookie/nsCookieModule.cpp
index 133f5ca00e02..247a8b7cb8de 100644
--- a/extensions/cookie/nsCookieModule.cpp
+++ b/extensions/cookie/nsCookieModule.cpp
@@ -10,7 +10,7 @@
 #include "nsPopupWindowManager.h"
 #include "nsICategoryManager.h"
 #include "nsCookiePermission.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 
 // Define the constructor function for the objects
 NS_GENERIC_FACTORY_SINGLETON_CONSTRUCTOR(nsIPermissionManager,
diff --git a/extensions/permissions/nsModuleFactory.cpp b/extensions/permissions/nsModuleFactory.cpp
index a8917c463492..9df69ea371df 100644
--- a/extensions/permissions/nsModuleFactory.cpp
+++ b/extensions/permissions/nsModuleFactory.cpp
@@ -5,7 +5,7 @@
 #include "mozilla/ModuleUtils.h"
 #include "nsIServiceManager.h"
 #include "nsContentBlocker.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 
 // Define the constructor function for the objects
 NS_GENERIC_FACTORY_CONSTRUCTOR_INIT(nsContentBlocker, Init)
diff --git a/extensions/pref/autoconfig/src/nsReadConfig.cpp b/extensions/pref/autoconfig/src/nsReadConfig.cpp
index 78d7b2d19bde..f14b7c9920d1 100644
--- a/extensions/pref/autoconfig/src/nsReadConfig.cpp
+++ b/extensions/pref/autoconfig/src/nsReadConfig.cpp
@@ -17,7 +17,6 @@
 #include "nsIServiceManager.h"
 #include "nsIStringBundle.h"
 #include "nsToolkitCompsCID.h"
-#include "nsXPIDLString.h"
 #include "nsNetUtil.h"
 #include "nsString.h"
 #include "nsCRT.h"
diff --git a/extensions/spellcheck/hunspell/glue/mozHunspell.cpp b/extensions/spellcheck/hunspell/glue/mozHunspell.cpp
index 890649f50133..64275ec49fc3 100644
--- a/extensions/spellcheck/hunspell/glue/mozHunspell.cpp
+++ b/extensions/spellcheck/hunspell/glue/mozHunspell.cpp
@@ -59,7 +59,7 @@
 
 #include "mozHunspell.h"
 #include "nsReadableUtils.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsIObserverService.h"
 #include "nsISimpleEnumerator.h"
 #include "nsIDirectoryEnumerator.h"
diff --git a/image/decoders/icon/mac/nsIconChannel.h b/image/decoders/icon/mac/nsIconChannel.h
index 208f556d2e72..9a8b010d61bf 100644
--- a/image/decoders/icon/mac/nsIconChannel.h
+++ b/image/decoders/icon/mac/nsIconChannel.h
@@ -10,7 +10,7 @@
 #include "mozilla/Attributes.h"
 
 #include "nsCOMPtr.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsIChannel.h"
 #include "nsILoadGroup.h"
 #include "nsILoadInfo.h"
diff --git a/image/decoders/icon/mac/nsIconChannelCocoa.mm b/image/decoders/icon/mac/nsIconChannelCocoa.mm
index cda8d3742ef2..53e93d4ff126 100644
--- a/image/decoders/icon/mac/nsIconChannelCocoa.mm
+++ b/image/decoders/icon/mac/nsIconChannelCocoa.mm
@@ -11,7 +11,7 @@
 #include "nsIServiceManager.h"
 #include "nsIInterfaceRequestor.h"
 #include "nsIInterfaceRequestorUtils.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsMimeTypes.h"
 #include "nsMemory.h"
 #include "nsIStringStream.h"
diff --git a/image/decoders/icon/win/nsIconChannel.cpp b/image/decoders/icon/win/nsIconChannel.cpp
index da1215c0738b..c137d7130522 100644
--- a/image/decoders/icon/win/nsIconChannel.cpp
+++ b/image/decoders/icon/win/nsIconChannel.cpp
@@ -11,7 +11,7 @@
 #include "nsIServiceManager.h"
 #include "nsIInterfaceRequestor.h"
 #include "nsIInterfaceRequestorUtils.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsMimeTypes.h"
 #include "nsMemory.h"
diff --git a/image/decoders/icon/win/nsIconChannel.h b/image/decoders/icon/win/nsIconChannel.h
index 94df5a52e865..f9b8c228aa31 100644
--- a/image/decoders/icon/win/nsIconChannel.h
+++ b/image/decoders/icon/win/nsIconChannel.h
@@ -10,7 +10,7 @@
 #include "mozilla/Attributes.h"
 
 #include "nsCOMPtr.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsIChannel.h"
 #include "nsILoadGroup.h"
 #include "nsILoadInfo.h"
diff --git a/js/xpconnect/src/xpcprivate.h b/js/xpconnect/src/xpcprivate.h
index b283f1fac95a..ddf9395100d5 100644
--- a/js/xpconnect/src/xpcprivate.h
+++ b/js/xpconnect/src/xpcprivate.h
@@ -123,7 +123,6 @@
 #include "prcvar.h"
 #include "nsString.h"
 #include "nsReadableUtils.h"
-#include "nsXPIDLString.h"
 
 #include "MainThreadUtils.h"
 
diff --git a/layout/tools/layout-debug/src/nsRegressionTester.cpp b/layout/tools/layout-debug/src/nsRegressionTester.cpp
index c1b6eb72d1de..efd9763ac381 100644
--- a/layout/tools/layout-debug/src/nsRegressionTester.cpp
+++ b/layout/tools/layout-debug/src/nsRegressionTester.cpp
@@ -6,7 +6,7 @@
 #include "nsISupports.h"
 #include "nsRegressionTester.h"
 
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsIWindowWatcher.h"
 #include "nsPIDOMWindow.h"
diff --git a/layout/xul/nsMenuFrame.cpp b/layout/xul/nsMenuFrame.cpp
index e2600e39b7e0..db1edab35b5c 100644
--- a/layout/xul/nsMenuFrame.cpp
+++ b/layout/xul/nsMenuFrame.cpp
@@ -25,7 +25,7 @@
 #include "nsIServiceManager.h"
 #include "nsCSSFrameConstructor.h"
 #include "nsIDOMKeyEvent.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsUnicharUtils.h"
 #include "nsIStringBundle.h"
diff --git a/layout/xul/nsTextBoxFrame.cpp b/layout/xul/nsTextBoxFrame.cpp
index 8f58d1f865ba..645dab298901 100644
--- a/layout/xul/nsTextBoxFrame.cpp
+++ b/layout/xul/nsTextBoxFrame.cpp
@@ -20,7 +20,7 @@
 #include "nsNameSpaceManager.h"
 #include "nsBoxLayoutState.h"
 #include "nsMenuBarListener.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsIServiceManager.h"
 #include "nsIDOMElement.h"
 #include "nsIDOMXULLabelElement.h"
diff --git a/layout/xul/tree/nsTreeBodyFrame.cpp b/layout/xul/tree/nsTreeBodyFrame.cpp
index dfddffafb2e7..fa3b1c964247 100644
--- a/layout/xul/tree/nsTreeBodyFrame.cpp
+++ b/layout/xul/tree/nsTreeBodyFrame.cpp
@@ -43,7 +43,7 @@
 #include "mozilla/css/StyleRule.h"
 #include "nsCSSRendering.h"
 #include "nsIXULTemplateBuilder.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsContainerFrame.h"
 #include "nsView.h"
 #include "nsViewManager.h"
diff --git a/modules/libjar/nsJARProtocolHandler.cpp b/modules/libjar/nsJARProtocolHandler.cpp
index 268330c433f9..1e0dfb9bfdea 100644
--- a/modules/libjar/nsJARProtocolHandler.cpp
+++ b/modules/libjar/nsJARProtocolHandler.cpp
@@ -12,7 +12,6 @@
 #include "nsJARURI.h"
 #include "nsIURL.h"
 #include "nsJARChannel.h"
-#include "nsXPIDLString.h"
 #include "nsString.h"
 #include "nsNetCID.h"
 #include "nsIMIMEService.h"
diff --git a/modules/libpref/Preferences.cpp b/modules/libpref/Preferences.cpp
index 017a0b3bd735..6ef130cb5146 100644
--- a/modules/libpref/Preferences.cpp
+++ b/modules/libpref/Preferences.cpp
@@ -33,7 +33,7 @@
 #include "nsIStringEnumerator.h"
 #include "nsIZipReader.h"
 #include "nsPrefBranch.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsCRT.h"
 #include "nsCOMArray.h"
 #include "nsXPCOMCID.h"
diff --git a/modules/libpref/nsPrefBranch.cpp b/modules/libpref/nsPrefBranch.cpp
index b82073677afb..68d1d3636ab1 100644
--- a/modules/libpref/nsPrefBranch.cpp
+++ b/modules/libpref/nsPrefBranch.cpp
@@ -15,7 +15,6 @@
 #include "nsIDirectoryService.h"
 #include "nsString.h"
 #include "nsReadableUtils.h"
-#include "nsXPIDLString.h"
 #include "nsPrintfCString.h"
 #include "nsIStringBundle.h"
 #include "prefapi.h"
diff --git a/netwerk/streamconv/converters/nsBinHexDecoder.cpp b/netwerk/streamconv/converters/nsBinHexDecoder.cpp
index 79edb4a11baa..68226dfa4992 100644
--- a/netwerk/streamconv/converters/nsBinHexDecoder.cpp
+++ b/netwerk/streamconv/converters/nsBinHexDecoder.cpp
@@ -11,7 +11,7 @@
 #include "nsIPipe.h"
 #include "nsMimeTypes.h"
 #include "netCore.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "prnetdb.h"
 #include "nsIURI.h"
 #include "nsIURL.h"
diff --git a/netwerk/streamconv/converters/nsIndexedToHTML.cpp b/netwerk/streamconv/converters/nsIndexedToHTML.cpp
index 9631113ac496..05b8351d5bca 100644
--- a/netwerk/streamconv/converters/nsIndexedToHTML.cpp
+++ b/netwerk/streamconv/converters/nsIndexedToHTML.cpp
@@ -22,7 +22,7 @@
 #include "nsIPrefLocalizedString.h"
 #include "nsIStringBundle.h"
 #include "nsITextToSubURI.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include <algorithm>
 #include "nsIChannel.h"
 
diff --git a/parser/html/nsParserUtils.cpp b/parser/html/nsParserUtils.cpp
index 186b057deeb1..bcaf0af24be9 100644
--- a/parser/html/nsParserUtils.cpp
+++ b/parser/html/nsParserUtils.cpp
@@ -8,7 +8,6 @@
 #include "nsCOMPtr.h"
 #include "nsXPCOM.h"
 #include "nsISupportsPrimitives.h"
-#include "nsXPIDLString.h"
 #include "nsEscape.h"
 #include "nsIParser.h"
 #include "nsIDTD.h"
diff --git a/parser/htmlparser/nsParserMsgUtils.cpp b/parser/htmlparser/nsParserMsgUtils.cpp
index 43d2e64d844e..1a6b18da2e03 100644
--- a/parser/htmlparser/nsParserMsgUtils.cpp
+++ b/parser/htmlparser/nsParserMsgUtils.cpp
@@ -5,7 +5,7 @@
 
 #include "nsIServiceManager.h"
 #include "nsIStringBundle.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsParserMsgUtils.h"
 #include "nsNetCID.h"
 #include "mozilla/Services.h"
diff --git a/rdf/base/nsCompositeDataSource.cpp b/rdf/base/nsCompositeDataSource.cpp
index 4b5ba872bc9d..1cefa9319c4b 100644
--- a/rdf/base/nsCompositeDataSource.cpp
+++ b/rdf/base/nsCompositeDataSource.cpp
@@ -36,7 +36,7 @@
 #include "nsTArray.h"
 #include "nsCOMArray.h"
 #include "nsArrayEnumerator.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "rdf.h"
 #include "nsCycleCollectionParticipant.h"
 
diff --git a/rdf/base/nsContainerEnumerator.cpp b/rdf/base/nsContainerEnumerator.cpp
index 57af387d3189..19700a9e1c0a 100644
--- a/rdf/base/nsContainerEnumerator.cpp
+++ b/rdf/base/nsContainerEnumerator.cpp
@@ -29,7 +29,6 @@
 #include "nsIServiceManager.h"
 #include "nsRDFCID.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "mozilla/Logging.h"
 #include "rdf.h"
 #include "rdfutil.h"
diff --git a/rdf/base/nsInMemoryDataSource.cpp b/rdf/base/nsInMemoryDataSource.cpp
index e2ff154878ec..0c75c5f5643f 100644
--- a/rdf/base/nsInMemoryDataSource.cpp
+++ b/rdf/base/nsInMemoryDataSource.cpp
@@ -44,7 +44,7 @@
 #include "nsRDFBaseDataSources.h"
 #include "nsString.h"
 #include "nsReadableUtils.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "rdfutil.h"
 #include "PLDHashTable.h"
 #include "plstr.h"
diff --git a/rdf/base/nsRDFContainer.cpp b/rdf/base/nsRDFContainer.cpp
index 0ba363c907f9..1ef97ab0f0d3 100644
--- a/rdf/base/nsRDFContainer.cpp
+++ b/rdf/base/nsRDFContainer.cpp
@@ -42,7 +42,6 @@
 #include "nsIServiceManager.h"
 #include "nsRDFCID.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "rdf.h"
 
 #define RDF_SEQ_LIST_LIMIT   8
diff --git a/rdf/base/nsRDFContainerUtils.cpp b/rdf/base/nsRDFContainerUtils.cpp
index b22754a3aeba..d92f00c3e8a9 100644
--- a/rdf/base/nsRDFContainerUtils.cpp
+++ b/rdf/base/nsRDFContainerUtils.cpp
@@ -17,7 +17,6 @@
 #include "nsIRDFService.h"
 #include "nsRDFCID.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "plstr.h"
 #include "rdf.h"
 #include "rdfutil.h"
diff --git a/rdf/base/nsRDFContentSink.cpp b/rdf/base/nsRDFContentSink.cpp
index c92cf86e9afd..28a6b7d775c6 100644
--- a/rdf/base/nsRDFContentSink.cpp
+++ b/rdf/base/nsRDFContentSink.cpp
@@ -52,7 +52,7 @@
 #include "nsIXMLContentSink.h"
 #include "nsRDFCID.h"
 #include "nsTArray.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "mozilla/Logging.h"
 #include "rdf.h"
 #include "rdfutil.h"
diff --git a/rdf/base/nsRDFService.cpp b/rdf/base/nsRDFService.cpp
index 6146f11f9496..6ca488eff5ac 100644
--- a/rdf/base/nsRDFService.cpp
+++ b/rdf/base/nsRDFService.cpp
@@ -30,7 +30,6 @@
 #include "nsIFactory.h"
 #include "nsRDFCID.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "nsNetUtil.h"
 #include "nsIURI.h"
 #include "PLDHashTable.h"
diff --git a/rdf/base/nsRDFXMLDataSource.cpp b/rdf/base/nsRDFXMLDataSource.cpp
index 05a5aea2b55b..d893b9d2c825 100644
--- a/rdf/base/nsRDFXMLDataSource.cpp
+++ b/rdf/base/nsRDFXMLDataSource.cpp
@@ -81,7 +81,7 @@
 #include "nsRDFCID.h"
 #include "nsRDFBaseDataSources.h"
 #include "nsCOMArray.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "plstr.h"
 #include "prio.h"
 #include "prthread.h"
diff --git a/rdf/base/nsRDFXMLSerializer.cpp b/rdf/base/nsRDFXMLSerializer.cpp
index 32c46176f421..a0e1747ec752 100644
--- a/rdf/base/nsRDFXMLSerializer.cpp
+++ b/rdf/base/nsRDFXMLSerializer.cpp
@@ -13,7 +13,6 @@
 #include "nsIRDFContainerUtils.h"
 #include "nsIServiceManager.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "nsTArray.h"
 #include "rdf.h"
 #include "rdfutil.h"
diff --git a/rdf/base/nsRDFXMLSerializer.h b/rdf/base/nsRDFXMLSerializer.h
index 96cac399d5b9..3cb442ba6c39 100644
--- a/rdf/base/nsRDFXMLSerializer.h
+++ b/rdf/base/nsRDFXMLSerializer.h
@@ -11,7 +11,7 @@
 #include "nsIRDFXMLSerializer.h"
 #include "nsIRDFXMLSource.h"
 #include "nsNameSpaceMap.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 
 #include "nsDataHashtable.h"
 #include "rdfITripleVisitor.h"
diff --git a/rdf/base/rdfutil.cpp b/rdf/base/rdfutil.cpp
index cba56a9780a0..191ee68d1a26 100644
--- a/rdf/base/rdfutil.cpp
+++ b/rdf/base/rdfutil.cpp
@@ -29,7 +29,6 @@
 #include "nsIURL.h"
 #include "nsRDFCID.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "nsUnicharUtils.h"
 #include "rdfutil.h"
 #include "prtime.h"
diff --git a/rdf/datasource/nsFileSystemDataSource.cpp b/rdf/datasource/nsFileSystemDataSource.cpp
index f208bd16028b..f2b9d364a3f5 100644
--- a/rdf/datasource/nsFileSystemDataSource.cpp
+++ b/rdf/datasource/nsFileSystemDataSource.cpp
@@ -16,7 +16,7 @@
 #include "nsIRDFDataSource.h"
 #include "nsIRDFObserver.h"
 #include "nsIServiceManager.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsRDFCID.h"
 #include "rdfutil.h"
 #include "rdf.h"
diff --git a/rdf/datasource/nsLocalStore.cpp b/rdf/datasource/nsLocalStore.cpp
index 8e2696a0f315..38cb27fe4b2b 100644
--- a/rdf/datasource/nsLocalStore.cpp
+++ b/rdf/datasource/nsLocalStore.cpp
@@ -22,7 +22,7 @@
 #include "nsIRDFService.h"
 #include "nsIServiceManager.h"
 #include "nsRDFCID.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "plstr.h"
 #include "rdf.h"
 #include "nsCOMPtr.h"
diff --git a/security/manager/ssl/nsCertTree.cpp b/security/manager/ssl/nsCertTree.cpp
index 50f4db0ee7bc..ce76b54fdf5a 100644
--- a/security/manager/ssl/nsCertTree.cpp
+++ b/security/manager/ssl/nsCertTree.cpp
@@ -23,7 +23,7 @@
 #include "nsTHashtable.h"
 #include "nsUnicharUtils.h"
 #include "nsXPCOMCID.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "pkix/pkixtypes.h"
 
 using namespace mozilla;
diff --git a/security/manager/ssl/nsSSLStatus.h b/security/manager/ssl/nsSSLStatus.h
index 2a8343407da3..aff74f13bdf2 100644
--- a/security/manager/ssl/nsSSLStatus.h
+++ b/security/manager/ssl/nsSSLStatus.h
@@ -10,7 +10,7 @@
 #include "CertVerifier.h" // For CertificateTransparencyInfo
 #include "nsISSLStatus.h"
 #include "nsCOMPtr.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsIX509Cert.h"
 #include "nsISerializable.h"
 #include "nsIClassInfo.h"
diff --git a/toolkit/components/alerts/nsAlertsUtils.cpp b/toolkit/components/alerts/nsAlertsUtils.cpp
index 5f7d92d2aa0d..e72415c87671 100644
--- a/toolkit/components/alerts/nsAlertsUtils.cpp
+++ b/toolkit/components/alerts/nsAlertsUtils.cpp
@@ -8,7 +8,7 @@
 #include "nsContentUtils.h"
 #include "nsIStringBundle.h"
 #include "nsIURI.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 
 /* static */
 bool
diff --git a/toolkit/components/browser/build/nsWebBrowserModule.cpp b/toolkit/components/browser/build/nsWebBrowserModule.cpp
index a061a2b4349d..4fe167d28628 100644
--- a/toolkit/components/browser/build/nsWebBrowserModule.cpp
+++ b/toolkit/components/browser/build/nsWebBrowserModule.cpp
@@ -6,7 +6,7 @@
 
 #include "mozilla/ModuleUtils.h"
 #include "nsIServiceManager.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 
 #include "nsEmbedCID.h"
 
diff --git a/toolkit/components/find/nsWebBrowserFind.cpp b/toolkit/components/find/nsWebBrowserFind.cpp
index 4b73f433aff7..08dc3a437dfe 100644
--- a/toolkit/components/find/nsWebBrowserFind.cpp
+++ b/toolkit/components/find/nsWebBrowserFind.cpp
@@ -43,7 +43,7 @@
 
 #if DEBUG
 #include "nsIWebNavigation.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #endif
 
 nsWebBrowserFind::nsWebBrowserFind()
diff --git a/toolkit/components/printingui/ipc/PrintDataUtils.cpp b/toolkit/components/printingui/ipc/PrintDataUtils.cpp
index f141a58cb43d..6dca09e61ba0 100644
--- a/toolkit/components/printingui/ipc/PrintDataUtils.cpp
+++ b/toolkit/components/printingui/ipc/PrintDataUtils.cpp
@@ -8,7 +8,7 @@
 #include "nsIPrintSettings.h"
 #include "nsIServiceManager.h"
 #include "nsIWebBrowserPrint.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 
 namespace mozilla {
 namespace embedding {
diff --git a/toolkit/components/startup/nsUserInfoUnix.cpp b/toolkit/components/startup/nsUserInfoUnix.cpp
index 5def34408870..158ac9bbf14a 100644
--- a/toolkit/components/startup/nsUserInfoUnix.cpp
+++ b/toolkit/components/startup/nsUserInfoUnix.cpp
@@ -12,7 +12,6 @@
 #include <sys/utsname.h>
 
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "nsReadableUtils.h"
 #include "nsNativeCharsetUtils.h"
 
diff --git a/toolkit/components/startup/nsUserInfoWin.cpp b/toolkit/components/startup/nsUserInfoWin.cpp
index b27a2c483b1c..99e104240189 100644
--- a/toolkit/components/startup/nsUserInfoWin.cpp
+++ b/toolkit/components/startup/nsUserInfoWin.cpp
@@ -9,7 +9,6 @@
 #include "nsString.h"
 #include "windows.h"
 #include "nsCRT.h"
-#include "nsXPIDLString.h"
 
 #define SECURITY_WIN32
 #include "lm.h"
diff --git a/toolkit/xre/nsAppRunner.cpp b/toolkit/xre/nsAppRunner.cpp
index a01f66ff8171..4870ee219138 100644
--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -133,7 +133,7 @@
 #include "nsReadableUtils.h"
 #include "nsXPCOM.h"
 #include "nsXPCOMCIDInternal.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsPrintfCString.h"
 #include "nsVersionComparator.h"
 
diff --git a/toolkit/xre/nsAppStartupNotifier.cpp b/toolkit/xre/nsAppStartupNotifier.cpp
index 4aed036936e7..f66067640fd4 100644
--- a/toolkit/xre/nsAppStartupNotifier.cpp
+++ b/toolkit/xre/nsAppStartupNotifier.cpp
@@ -5,7 +5,6 @@
 
 #include "nsCOMPtr.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "nsIServiceManager.h"
 #include "nsICategoryManager.h"
 #include "nsXPCOM.h"
diff --git a/toolkit/xre/nsNativeAppSupportWin.cpp b/toolkit/xre/nsNativeAppSupportWin.cpp
index 2400d15248fa..d02754f8e3fc 100644
--- a/toolkit/xre/nsNativeAppSupportWin.cpp
+++ b/toolkit/xre/nsNativeAppSupportWin.cpp
@@ -12,7 +12,6 @@
 #include "nsIBrowserDOMWindow.h"
 #include "nsICommandLineRunner.h"
 #include "nsCOMPtr.h"
-#include "nsXPIDLString.h"
 #include "nsIComponentManager.h"
 #include "nsIServiceManager.h"
 #include "nsIDOMChromeWindow.h"
diff --git a/uriloader/base/nsDocLoader.cpp b/uriloader/base/nsDocLoader.cpp
index 229550088fd1..7d345fa71f91 100644
--- a/uriloader/base/nsDocLoader.cpp
+++ b/uriloader/base/nsDocLoader.cpp
@@ -15,7 +15,7 @@
 #include "nsIWebProgressListener2.h"
 
 #include "nsIServiceManager.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 
 #include "nsIURL.h"
 #include "nsCOMPtr.h"
diff --git a/uriloader/base/nsURILoader.cpp b/uriloader/base/nsURILoader.cpp
index fd26e90787d3..a2a456261e2a 100644
--- a/uriloader/base/nsURILoader.cpp
+++ b/uriloader/base/nsURILoader.cpp
@@ -32,7 +32,6 @@
 #include "nsIDocShellTreeOwner.h"
 #include "nsIThreadRetargetableStreamListener.h"
 
-#include "nsXPIDLString.h"
 #include "nsString.h"
 #include "nsThreadUtils.h"
 #include "nsReadableUtils.h"
diff --git a/uriloader/exthandler/mac/nsOSHelperAppService.mm b/uriloader/exthandler/mac/nsOSHelperAppService.mm
index 4794a8fcb008..b1b0c9ce1cbd 100644
--- a/uriloader/exthandler/mac/nsOSHelperAppService.mm
+++ b/uriloader/exthandler/mac/nsOSHelperAppService.mm
@@ -11,7 +11,6 @@
 #include "nsISupports.h"
 #include "nsString.h"
 #include "nsTArray.h"
-#include "nsXPIDLString.h"
 #include "nsIURL.h"
 #include "nsIFile.h"
 #include "nsILocalFileMac.h"
diff --git a/uriloader/exthandler/nsExternalHelperAppService.cpp b/uriloader/exthandler/nsExternalHelperAppService.cpp
index 28b7a21b1f0e..2bf3e927f2ab 100644
--- a/uriloader/exthandler/nsExternalHelperAppService.cpp
+++ b/uriloader/exthandler/nsExternalHelperAppService.cpp
@@ -25,7 +25,7 @@
 #include "nsAppDirectoryServiceDefs.h"
 #include "nsICategoryManager.h"
 #include "nsDependentSubstring.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsUnicharUtils.h"
 #include "nsIStringEnumerator.h"
 #include "nsMemory.h"
diff --git a/uriloader/exthandler/nsExternalProtocolHandler.cpp b/uriloader/exthandler/nsExternalProtocolHandler.cpp
index 2ab27c37d90f..d5c81caf7c32 100644
--- a/uriloader/exthandler/nsExternalProtocolHandler.cpp
+++ b/uriloader/exthandler/nsExternalProtocolHandler.cpp
@@ -8,7 +8,7 @@
 #include "nsIURI.h"
 #include "nsIURL.h"
 #include "nsExternalProtocolHandler.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsCOMPtr.h"
 #include "nsContentUtils.h"
diff --git a/uriloader/exthandler/nsMIMEInfoImpl.cpp b/uriloader/exthandler/nsMIMEInfoImpl.cpp
index 59886e4651ab..b312cd576d26 100644
--- a/uriloader/exthandler/nsMIMEInfoImpl.cpp
+++ b/uriloader/exthandler/nsMIMEInfoImpl.cpp
@@ -5,7 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsMIMEInfoImpl.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsStringEnumerator.h"
 #include "nsIFile.h"
diff --git a/uriloader/exthandler/unix/nsOSHelperAppService.cpp b/uriloader/exthandler/unix/nsOSHelperAppService.cpp
index e1ac2582e65b..721836982df5 100644
--- a/uriloader/exthandler/unix/nsOSHelperAppService.cpp
+++ b/uriloader/exthandler/unix/nsOSHelperAppService.cpp
@@ -21,7 +21,6 @@
 #include "nsString.h"
 #include "nsReadableUtils.h"
 #include "nsUnicharUtils.h"
-#include "nsXPIDLString.h"
 #include "nsIURL.h"
 #include "nsIFileStreams.h"
 #include "nsILineInputStream.h"
diff --git a/uriloader/exthandler/win/nsOSHelperAppService.cpp b/uriloader/exthandler/win/nsOSHelperAppService.cpp
index ffc35f7dfd18..b68e35257a7f 100644
--- a/uriloader/exthandler/win/nsOSHelperAppService.cpp
+++ b/uriloader/exthandler/win/nsOSHelperAppService.cpp
@@ -8,7 +8,6 @@
 #include "nsOSHelperAppService.h"
 #include "nsISupports.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "nsIURL.h"
 #include "nsIMIMEInfo.h"
 #include "nsMIMEInfoWin.h"
diff --git a/uriloader/prefetch/nsPrefetchService.cpp b/uriloader/prefetch/nsPrefetchService.cpp
index 74ae3955c97f..3b5983c03ffe 100644
--- a/uriloader/prefetch/nsPrefetchService.cpp
+++ b/uriloader/prefetch/nsPrefetchService.cpp
@@ -24,7 +24,6 @@
 #include "nsISupportsPriority.h"
 #include "nsNetUtil.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "nsReadableUtils.h"
 #include "nsStreamUtils.h"
 #include "nsAutoPtr.h"
diff --git a/widget/cocoa/nsClipboard.h b/widget/cocoa/nsClipboard.h
index d47bfeb449ac..6b0928b628b8 100644
--- a/widget/cocoa/nsClipboard.h
+++ b/widget/cocoa/nsClipboard.h
@@ -7,7 +7,7 @@
 #define nsClipboard_h_
 
 #include "nsIClipboard.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "mozilla/StaticPtr.h"
 
 #import <Cocoa/Cocoa.h>
diff --git a/widget/cocoa/nsClipboard.mm b/widget/cocoa/nsClipboard.mm
index 2ae118f3ccac..b36ecc1f9ad6 100644
--- a/widget/cocoa/nsClipboard.mm
+++ b/widget/cocoa/nsClipboard.mm
@@ -13,7 +13,6 @@
 #include "nsClipboard.h"
 #include "nsString.h"
 #include "nsISupportsPrimitives.h"
-#include "nsXPIDLString.h"
 #include "nsPrimitiveHelpers.h"
 #include "nsMemory.h"
 #include "nsIFile.h"
diff --git a/widget/gtk/nsClipboard.cpp b/widget/gtk/nsClipboard.cpp
index 73ea5288539c..fd7affc41ad5 100644
--- a/widget/gtk/nsClipboard.cpp
+++ b/widget/gtk/nsClipboard.cpp
@@ -12,7 +12,6 @@
 #include "nsSupportsPrimitives.h"
 #include "nsString.h"
 #include "nsReadableUtils.h"
-#include "nsXPIDLString.h"
 #include "nsPrimitiveHelpers.h"
 #include "nsIServiceManager.h"
 #include "nsImageToPixbuf.h"
diff --git a/widget/gtk/nsWindow.cpp b/widget/gtk/nsWindow.cpp
index 835d2295da22..dcb9a3fc9756 100644
--- a/widget/gtk/nsWindow.cpp
+++ b/widget/gtk/nsWindow.cpp
@@ -97,7 +97,7 @@ using namespace mozilla::widget;
 
 /* For SetIcon */
 #include "nsAppDirectoryServiceDefs.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsIFile.h"
 
 /* SetCursor(imgIContainer*) */
diff --git a/widget/nsBaseFilePicker.cpp b/widget/nsBaseFilePicker.cpp
index 7afbaaaaaaed..ddd17c9d10a2 100644
--- a/widget/nsBaseFilePicker.cpp
+++ b/widget/nsBaseFilePicker.cpp
@@ -12,7 +12,7 @@
 #include "nsIWidget.h"
 
 #include "nsIStringBundle.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsIServiceManager.h"
 #include "nsCOMArray.h"
 #include "nsIFile.h"
diff --git a/widget/nsTransferable.cpp b/widget/nsTransferable.cpp
index 7817da11b29c..06dba461a198 100644
--- a/widget/nsTransferable.cpp
+++ b/widget/nsTransferable.cpp
@@ -27,7 +27,6 @@ Notes to self:
 #include "nsISupportsPrimitives.h"
 #include "nsMemory.h"
 #include "nsPrimitiveHelpers.h"
-#include "nsXPIDLString.h"
 #include "nsDirectoryServiceDefs.h"
 #include "nsDirectoryService.h"
 #include "nsCRT.h"
diff --git a/widget/windows/nsClipboard.cpp b/widget/windows/nsClipboard.cpp
index 3a3224a3b6c5..cf72a72fe9ae 100644
--- a/widget/windows/nsClipboard.cpp
+++ b/widget/windows/nsClipboard.cpp
@@ -22,7 +22,6 @@
 #include "nsCOMPtr.h"
 #include "nsXPCOM.h"
 #include "nsISupportsPrimitives.h"
-#include "nsXPIDLString.h"
 #include "nsReadableUtils.h"
 #include "nsUnicharUtils.h"
 #include "nsPrimitiveHelpers.h"
diff --git a/widget/windows/nsDataObj.cpp b/widget/windows/nsDataObj.cpp
index 12fa69bfa37f..e85d90053484 100644
--- a/widget/windows/nsDataObj.cpp
+++ b/widget/windows/nsDataObj.cpp
@@ -16,7 +16,7 @@
 #include "nsISupportsPrimitives.h"
 #include "IEnumFE.h"
 #include "nsPrimitiveHelpers.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsImageClipboard.h"
 #include "nsCRT.h"
 #include "nsPrintfCString.h"
diff --git a/widget/windows/nsWindow.cpp b/widget/windows/nsWindow.cpp
index 74a275aed451..21428ee8c184 100644
--- a/widget/windows/nsWindow.cpp
+++ b/widget/windows/nsWindow.cpp
@@ -105,7 +105,6 @@
 #include "nsGkAtoms.h"
 #include "nsCRT.h"
 #include "nsAppDirectoryServiceDefs.h"
-#include "nsXPIDLString.h"
 #include "nsWidgetsCID.h"
 #include "nsTHashtable.h"
 #include "nsHashKeys.h"
diff --git a/xpcom/components/nsComponentManager.cpp b/xpcom/components/nsComponentManager.cpp
index c48cdb5da388..ca938f7ed0e2 100644
--- a/xpcom/components/nsComponentManager.cpp
+++ b/xpcom/components/nsComponentManager.cpp
@@ -31,7 +31,6 @@
 #include "nsLocalFile.h"
 #include "nsReadableUtils.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "prcmon.h"
 #include "xptinfo.h" // this after nsISupports, to pick up IID so that xpt stuff doesn't try to define it itself...
 #include "nsThreadUtils.h"
diff --git a/xpcom/io/nsAppFileLocationProvider.cpp b/xpcom/io/nsAppFileLocationProvider.cpp
index 5ad4686f08d1..29fbf53ca8cb 100644
--- a/xpcom/io/nsAppFileLocationProvider.cpp
+++ b/xpcom/io/nsAppFileLocationProvider.cpp
@@ -11,7 +11,6 @@
 #include "nsIAtom.h"
 #include "nsIFile.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "nsISimpleEnumerator.h"
 #include "prenv.h"
 #include "nsCRT.h"
diff --git a/xpcom/io/nsLocalFileUnix.cpp b/xpcom/io/nsLocalFileUnix.cpp
index 8f4d61d3aa9c..8aa407829d64 100644
--- a/xpcom/io/nsLocalFileUnix.cpp
+++ b/xpcom/io/nsLocalFileUnix.cpp
@@ -42,7 +42,6 @@
 #include "nsReadableUtils.h"
 #include "nsLocalFile.h"
 #include "nsIComponentManager.h"
-#include "nsXPIDLString.h"
 #include "prproces.h"
 #include "nsIDirectoryEnumerator.h"
 #include "nsISimpleEnumerator.h"
diff --git a/xpcom/io/nsLocalFileWin.cpp b/xpcom/io/nsLocalFileWin.cpp
index db127eaf0a7a..0d26b6e4a574 100755
--- a/xpcom/io/nsLocalFileWin.cpp
+++ b/xpcom/io/nsLocalFileWin.cpp
@@ -23,7 +23,7 @@
 #include "private/pprio.h"  // To get PR_ImportFile
 #include "nsHashKeys.h"
 
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsReadableUtils.h"
 
 #include <direct.h>
@@ -39,7 +39,6 @@
 #include  <stdlib.h>
 #include  <mbstring.h>
 
-#include "nsXPIDLString.h"
 #include "prproces.h"
 #include "prlink.h"
 
diff --git a/xpcom/reflect/xptinfo/xptiprivate.h b/xpcom/reflect/xptinfo/xptiprivate.h
index c32ef9c77aa4..ff9a3c5d0a40 100644
--- a/xpcom/reflect/xptinfo/xptiprivate.h
+++ b/xpcom/reflect/xptinfo/xptiprivate.h
@@ -41,7 +41,7 @@
 #include "nsCOMArray.h"
 #include "nsQuickSort.h"
 
-#include "nsXPIDLString.h"
+#include "nsString.h"
 
 #include "nsIInputStream.h"
 
diff --git a/xpcom/string/moz.build b/xpcom/string/moz.build
index 0cd7574dafa4..8cdd2cceeb06 100644
--- a/xpcom/string/moz.build
+++ b/xpcom/string/moz.build
@@ -32,7 +32,6 @@ EXPORTS += [
     'nsTSubstring.h',
     'nsTSubstringTuple.h',
     'nsUTF8Utils.h',
-    'nsXPIDLString.h',
     'string-template-def-char.h',
     'string-template-def-unichar.h',
     'string-template-undef.h',
diff --git a/xpcom/string/nsStringFwd.h b/xpcom/string/nsStringFwd.h
index f9d57c0d7c18..89c7c03b4df8 100644
--- a/xpcom/string/nsStringFwd.h
+++ b/xpcom/string/nsStringFwd.h
@@ -45,6 +45,5 @@ class nsDependentCSubstring;
 class nsPromiseFlatCString;
 class nsCStringComparator;
 class nsDefaultCStringComparator;
-class nsXPIDLCString; // deprecated
 
 #endif /* !defined(nsStringFwd_h) */
diff --git a/xpcom/string/nsTString.h b/xpcom/string/nsTString.h
index fc42668a361a..2cce848342e3 100644
--- a/xpcom/string/nsTString.h
+++ b/xpcom/string/nsTString.h
@@ -699,92 +699,6 @@ public:
   }
 };
 
-/**
- * nsTXPIDLString extends nsTString such that:
- *
- *   (1) mData can be null
- *   (2) objects of this type can be automatically cast to |const CharT*|
- *   (3) getter_Copies method is supported to adopt data allocated with
- *       moz_xmalloc, such as "out string" parameters in XPIDL.
- *
- * NAMES:
- *   nsXPIDLString for wide characters (no longer available)
- *   nsXPIDLCString for narrow characters (deprecated)
- */
-class nsTXPIDLString_CharT : public nsTString_CharT
-{
-public:
-
-  typedef nsTXPIDLString_CharT self_type;
-
-public:
-
-  nsTXPIDLString_CharT()
-    : string_type(char_traits::sEmptyBuffer, 0,
-                  DataFlags::TERMINATED | DataFlags::VOIDED, ClassFlags(0))
-  {
-  }
-
-  // copy-constructor required to avoid default
-  nsTXPIDLString_CharT(const self_type& aStr)
-    : string_type(char_traits::sEmptyBuffer, 0,
-                  DataFlags::TERMINATED | DataFlags::VOIDED, ClassFlags(0))
-  {
-    Assign(aStr);
-  }
-
-  // return nullptr if we are voided
-#if defined(CharT_is_PRUnichar) && defined(MOZ_USE_CHAR16_WRAPPER)
-  MOZ_NO_DANGLING_ON_TEMPORARIES char16ptr_t get() const
-#else
-  MOZ_NO_DANGLING_ON_TEMPORARIES const char_type* get() const
-#endif
-  {
-    return (mDataFlags & DataFlags::VOIDED) ? nullptr : mData;
-  }
-
-  // this case operator is the reason why this class cannot just be a
-  // typedef for nsTString
-  operator const char_type*() const
-  {
-    return get();
-  }
-
-  // need this to diambiguous operator[int]
-  char_type operator[](int32_t aIndex) const
-  {
-    return CharAt(index_type(aIndex));
-  }
-
-  // |operator=| does not inherit, so we must define our own
-  self_type& operator=(char_type aChar)
-  {
-    Assign(aChar);
-    return *this;
-  }
-  self_type& operator=(const char_type* aStr)
-  {
-    Assign(aStr);
-    return *this;
-  }
-  self_type& operator=(const self_type& aStr)
-  {
-    Assign(aStr);
-    return *this;
-  }
-  self_type& operator=(const substring_type& aStr)
-  {
-    Assign(aStr);
-    return *this;
-  }
-  self_type& operator=(const substring_tuple_type& aTuple)
-  {
-    Assign(aTuple);
-    return *this;
-  }
-};
-
-
 /**
  * getter_Copies support for adopting raw string out params that are
  * heap-allocated, e.g.:
diff --git a/xpcom/string/nsXPIDLString.h b/xpcom/string/nsXPIDLString.h
deleted file mode 100644
index f5821cdb09e4..000000000000
--- a/xpcom/string/nsXPIDLString.h
+++ /dev/null
@@ -1,12 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* 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 nsXPIDLString_h___
-#define nsXPIDLString_h___
-
-#include "nsString.h"
-
-#endif /* !defined(nsXPIDLString_h___) */
diff --git a/xpcom/string/string-template-def-char.h b/xpcom/string/string-template-def-char.h
index 89a3340c0740..e142e38dc3fb 100644
--- a/xpcom/string/string-template-def-char.h
+++ b/xpcom/string/string-template-def-char.h
@@ -21,7 +21,6 @@
 #define nsTDependentString_CharT            nsDependentCString
 #define nsTDependentSubstring_CharT         nsDependentCSubstring
 #define nsTLiteralString_CharT              nsLiteralCString
-#define nsTXPIDLString_CharT                nsXPIDLCString
 #define nsTGetterCopies_CharT               nsCGetterCopies
 #define nsTPromiseFlatString_CharT          nsPromiseFlatCString
 #define TPromiseFlatString_CharT            PromiseFlatCString
diff --git a/xpcom/string/string-template-undef.h b/xpcom/string/string-template-undef.h
index 02ecb4430bd3..b3cbb6c38eb9 100644
--- a/xpcom/string/string-template-undef.h
+++ b/xpcom/string/string-template-undef.h
@@ -22,7 +22,6 @@
 #undef nsTDependentString_CharT
 #undef nsTDependentSubstring_CharT
 #undef nsTLiteralString_CharT
-#undef nsTXPIDLString_CharT
 #undef nsTGetterCopies_CharT
 #undef nsTPromiseFlatString_CharT
 #undef TPromiseFlatString_CharT
diff --git a/xpcom/tests/gtest/TestStrings.cpp b/xpcom/tests/gtest/TestStrings.cpp
index 0ba604258045..d9424a5eef76 100644
--- a/xpcom/tests/gtest/TestStrings.cpp
+++ b/xpcom/tests/gtest/TestStrings.cpp
@@ -472,45 +472,6 @@ TEST(Strings, concat_3)
   EXPECT_STREQ(result.get(), "abc");
 }
 
-TEST(Strings, xpidl_string)
-{
-  nsXPIDLCString a, b;
-  a = b;
-  EXPECT_TRUE(a == b);
-
-  a.Adopt(0);
-  EXPECT_TRUE(a == b);
-
-  a.Append("foopy");
-  a.Assign(b);
-  EXPECT_TRUE(a == b);
-
-  a.Insert("", 0);
-  a.Assign(b);
-  EXPECT_TRUE(a == b);
-
-  const char text[] = "hello world";
-  *getter_Copies(a) = NS_strdup(text);
-  EXPECT_STREQ(a, text);
-
-  b = a;
-  EXPECT_STREQ(a, b);
-
-  a.Adopt(0);
-  nsACString::const_iterator begin, end;
-  a.BeginReading(begin);
-  a.EndReading(end);
-  char *r = ToNewCString(Substring(begin, end));
-  EXPECT_STREQ(r, "");
-  free(r);
-
-  a.Adopt(0);
-  EXPECT_TRUE(a.IsVoid());
-
-  int32_t index = a.FindCharInSet("xyz");
-  EXPECT_EQ(index, kNotFound);
-}
-
 TEST(Strings, empty_assign)
 {
   nsCString a;
@@ -720,21 +681,40 @@ TEST(Strings, voided)
 {
   const char kData[] = "hello world";
 
-  nsXPIDLCString str;
-  EXPECT_FALSE(str);
-  EXPECT_TRUE(str.IsVoid());
+  nsCString str;
+  EXPECT_TRUE(!str.IsVoid());
   EXPECT_TRUE(str.IsEmpty());
-
-  str.Assign(kData);
-  EXPECT_STREQ(str, kData);
+  EXPECT_STREQ(str.get(), "");
 
   str.SetIsVoid(true);
-  EXPECT_FALSE(str);
   EXPECT_TRUE(str.IsVoid());
   EXPECT_TRUE(str.IsEmpty());
+  EXPECT_STREQ(str.get(), "");
+
+  str.Assign(kData);
+  EXPECT_TRUE(!str.IsVoid());
+  EXPECT_TRUE(!str.IsEmpty());
+  EXPECT_STREQ(str.get(), kData);
+
+  str.SetIsVoid(true);
+  EXPECT_TRUE(str.IsVoid());
+  EXPECT_TRUE(str.IsEmpty());
+  EXPECT_STREQ(str.get(), "");
 
   str.SetIsVoid(false);
-  EXPECT_STREQ(str, "");
+  EXPECT_TRUE(!str.IsVoid());
+  EXPECT_TRUE(str.IsEmpty());
+  EXPECT_STREQ(str.get(), "");
+
+  str.Assign(kData);
+  EXPECT_TRUE(!str.IsVoid());
+  EXPECT_TRUE(!str.IsEmpty());
+  EXPECT_STREQ(str.get(), kData);
+
+  str.Adopt(nullptr);
+  EXPECT_TRUE(str.IsVoid());
+  EXPECT_TRUE(str.IsEmpty());
+  EXPECT_STREQ(str.get(), "");
 }
 
 TEST(Strings, voided_autostr)
diff --git a/xpfe/appshell/nsWindowMediator.cpp b/xpfe/appshell/nsWindowMediator.cpp
index 372ccccc3251..64fbb72675ab 100644
--- a/xpfe/appshell/nsWindowMediator.cpp
+++ b/xpfe/appshell/nsWindowMediator.cpp
@@ -17,7 +17,6 @@
 #include "nsAppShellWindowEnumerator.h"
 #include "nsWindowMediator.h"
 #include "nsIWindowMediatorListener.h"
-#include "nsXPIDLString.h"
 #include "nsGlobalWindow.h"
 
 #include "nsIDocShell.h"
diff --git a/xpfe/appshell/nsWindowMediator.h b/xpfe/appshell/nsWindowMediator.h
index 7398f4c2b7dd..860c4b371b95 100644
--- a/xpfe/appshell/nsWindowMediator.h
+++ b/xpfe/appshell/nsWindowMediator.h
@@ -10,7 +10,7 @@
 #include "nsIWindowMediator.h"
 #include "nsIObserver.h"
 #include "nsTArray.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsWeakReference.h"
 #include "nsTObserverArray.h"
 
diff --git a/xpfe/components/directory/nsDirectoryViewer.cpp b/xpfe/components/directory/nsDirectoryViewer.cpp
index 4acce876ad85..4a1442199747 100644
--- a/xpfe/components/directory/nsDirectoryViewer.cpp
+++ b/xpfe/components/directory/nsDirectoryViewer.cpp
@@ -31,7 +31,6 @@
 #include "nsIXPConnect.h"
 #include "nsEnumeratorUtils.h"
 #include "nsString.h"
-#include "nsXPIDLString.h"
 #include "nsReadableUtils.h"
 #include "nsITextToSubURI.h"
 #include "nsIInterfaceRequestor.h"
diff --git a/xpfe/components/directory/nsDirectoryViewer.h b/xpfe/components/directory/nsDirectoryViewer.h
index d71647f22498..ecb32b0a1404 100644
--- a/xpfe/components/directory/nsDirectoryViewer.h
+++ b/xpfe/components/directory/nsDirectoryViewer.h
@@ -15,7 +15,7 @@
 #include "nsIRDFLiteral.h"
 #include "nsIDocumentLoaderFactory.h"
 #include "nsITimer.h"
-#include "nsXPIDLString.h"
+#include "nsString.h"
 #include "nsIDirIndexListener.h"
 #include "nsIFTPChannel.h"
 #include "nsCycleCollectionParticipant.h"