diff --git a/mozilla/Makefile.in b/mozilla/Makefile.in
index 6aa945baca1..88af9d4604a 100644
--- a/mozilla/Makefile.in
+++ b/mozilla/Makefile.in
@@ -140,10 +140,12 @@ endif
 tier_2_dirs	= \
 		js \
 		xpcom \
-		modules/libreg \
-		xpcom/obsolete \
 		$(NULL)
 
+ifndef MOZ_NO_XPCOM_OBSOLETE
+tier_2_dirs += modules/libreg xpcom/obsolete
+endif
+
 ifdef NS_TRACE_MALLOC
 tier_2_dirs	+= tools/trace-malloc/lib
 endif
diff --git a/mozilla/config/autoconf.mk.in b/mozilla/config/autoconf.mk.in
index b3d89cacc7c..a005d663d01 100644
--- a/mozilla/config/autoconf.mk.in
+++ b/mozilla/config/autoconf.mk.in
@@ -131,6 +131,7 @@ MOZ_IPCD = @MOZ_IPCD@
 MOZ_PROFILESHARING = @MOZ_PROFILESHARING@
 MOZ_PROFILELOCKING = @MOZ_PROFILELOCKING@
 MOZ_STORAGE = @MOZ_STORAGE@
+MOZ_NO_XPCOM_OBSOLETE = @MOZ_NO_XPCOM_OBSOLETE@
 
 MOZ_ENABLE_JAVAXPCOM = @MOZ_ENABLE_JAVAXPCOM@
 JAVA_INCLUDE_PATH=@JAVA_INCLUDE_PATH@
diff --git a/mozilla/configure.in b/mozilla/configure.in
index 754022ab219..e807d6223ef 100644
--- a/mozilla/configure.in
+++ b/mozilla/configure.in
@@ -3937,6 +3937,7 @@ MOZ_LIBART_LIBS=
 MOZ_MAIL_NEWS=
 MOZ_MATHML=1
 MOZ_NO_ACTIVEX_SUPPORT=1
+MOZ_NO_XPCOM_OBSOLETE=
 MOZ_OJI=1
 MOZ_PLAINTEXT_EDITOR_ONLY=
 MOZ_PLUGINS=1
@@ -4028,6 +4029,7 @@ minimo)
   MOZ_MAIL_NEWS=
   MOZ_MATHML=
   MOZ_NO_ACTIVEX_SUPPORT=1
+  MOZ_NO_XPCOM_OBSOLETE=1
   MOZ_OJI=
   MOZ_PLAINTEXT_EDITOR_ONLY=1
   MOZ_PROFILELOCKING=
@@ -4655,6 +4657,25 @@ MOZ_ARG_DISABLE_BOOL(composer,
     MOZ_COMPOSER=1 )
 AC_SUBST(MOZ_COMPOSER)
 
+
+dnl ========================================================
+dnl = Drop XPCOM Obsolete library
+dnl ========================================================
+MOZ_ARG_DISABLE_BOOL(xpcom-obsolete,
+[  --disable-xpcom-obsolete           Disable XPCOM Obsolete Library],
+    MOZ_NO_XPCOM_OBSOLETE=,
+    MOZ_NO_XPCOM_OBSOLETE=1)
+
+if test -n "$MOZ_NO_XPCOM_OBSOLETE"; then
+if test -n "$MOZ_XPINSTALL"; then
+    AC_MSG_ERROR([Building without xpcom-obsolete isn't support when building xpinstal.])
+fi
+if test -z "$MOZ_SINGLE_PROFILE"; then
+    AC_MSG_ERROR([Building without xpcom-obsolete isn't support when building full profile support.])
+fi
+    AC_DEFINE(MOZ_NO_XPCOM_OBSOLETE)
+fi
+
 dnl ========================================================
 dnl XTF
 dnl ========================================================
@@ -6630,6 +6651,7 @@ AC_SUBST(MOZ_EXTENSIONS)
 AC_SUBST(MOZ_IMG_DECODERS)
 AC_SUBST(MOZ_JSDEBUGGER)
 AC_SUBST(MOZ_OJI)
+AC_SUBST(MOZ_NO_XPCOM_OBSOLETE)
 AC_SUBST(MOZ_PLUGINS)
 AC_SUBST(ENABLE_EAZEL_PROFILER)
 AC_SUBST(EAZEL_PROFILER_CFLAGS)
diff --git a/mozilla/modules/libpref/src/nsPref.cpp b/mozilla/modules/libpref/src/nsPref.cpp
index f21e5265adb..3b6c48f3323 100644
--- a/mozilla/modules/libpref/src/nsPref.cpp
+++ b/mozilla/modules/libpref/src/nsPref.cpp
@@ -43,7 +43,11 @@
 #include "nsMemory.h"
 #include "prefapi.h"
 
+#ifndef MOZ_NO_XPCOM_OBSOLETE
 #include "nsIFileSpec.h"
+#endif
+
+#include "nsString.h"
 #include "nsILocalFile.h"
 #include "nsIPrefBranch.h"
 #include "nsIPrefLocalizedString.h"
@@ -477,16 +481,23 @@ NS_IMETHODIMP nsPref::GetDefaultLocalizedUnicharPref(const char *pref, PRUnichar
 
 NS_IMETHODIMP nsPref::GetFilePref(const char *pref, nsIFileSpec **_retval)
 {
+#ifdef MOZ_NO_XPCOM_OBSOLETE
+  return NS_ERROR_NOT_IMPLEMENTED;
+#else
   nsresult rv;
 
   nsCOMPtr<nsIPrefBranch> prefBranch = do_QueryInterface(mPrefService, &rv);
   if (NS_SUCCEEDED(rv))
     rv = prefBranch->GetComplexValue(pref, NS_GET_IID(nsIFileSpec), (void **)_retval);
   return rv;
+#endif
 }
 
 NS_IMETHODIMP nsPref::SetFilePref(const char *pref, nsIFileSpec *value, PRBool setDefault)
 {
+#ifdef MOZ_NO_XPCOM_OBSOLETE
+  return NS_ERROR_NOT_IMPLEMENTED;
+#else
   nsresult  rv;
 
   if (setDefault) {
@@ -497,6 +508,7 @@ NS_IMETHODIMP nsPref::SetFilePref(const char *pref, nsIFileSpec *value, PRBool s
       rv = prefBranch->SetComplexValue(pref, NS_GET_IID(nsIFileSpec), value);
   }
     return rv;
+#endif
 }
 
 NS_IMETHODIMP nsPref::GetFileXPref(const char *pref, nsILocalFile **_retval)
diff --git a/mozilla/modules/libpref/src/nsPrefBranch.cpp b/mozilla/modules/libpref/src/nsPrefBranch.cpp
index b9fafee0e54..8fc50850ac9 100644
--- a/mozilla/modules/libpref/src/nsPrefBranch.cpp
+++ b/mozilla/modules/libpref/src/nsPrefBranch.cpp
@@ -52,7 +52,13 @@
 #include "pldhash.h"
 #include "nsPrefsCID.h"
 
+#ifndef MOZ_NO_XPCOM_OBSOLETE
 #include "nsIFileSpec.h"  // this should be removed eventually
+#endif
+
+#include "plstr.h"
+#include "nsCRT.h"
+
 #include "prefapi_private_data.h"
 
 // Definitions
@@ -347,6 +353,7 @@ NS_IMETHODIMP nsPrefBranch::GetComplexValue(const char *aPrefName, const nsIID &
   }
 
   // This is deprecated and you should not be using it
+#ifndef MOZ_NO_XPCOM_OBSOLETE
   if (aType.Equals(NS_GET_IID(nsIFileSpec))) {
     nsCOMPtr<nsIFileSpec> file(do_CreateInstance(NS_FILESPEC_CONTRACTID, &rv));
 
@@ -366,6 +373,7 @@ NS_IMETHODIMP nsPrefBranch::GetComplexValue(const char *aPrefName, const nsIID &
     }
     return rv;
   }
+#endif
 
   NS_WARNING("nsPrefBranch::GetComplexValue - Unsupported interface type");
   return NS_NOINTERFACE;
@@ -447,6 +455,7 @@ NS_IMETHODIMP nsPrefBranch::SetComplexValue(const char *aPrefName, const nsIID &
     return rv;
   }
 
+#ifndef MOZ_NO_XPCOM_OBSOLETE
   // This is deprecated and you should not be using it
   if (aType.Equals(NS_GET_IID(nsIFileSpec))) {
     nsCOMPtr<nsIFileSpec> file = do_QueryInterface(aValue);
@@ -458,6 +467,7 @@ NS_IMETHODIMP nsPrefBranch::SetComplexValue(const char *aPrefName, const nsIID &
     }
     return rv;
   }
+#endif
 
   NS_WARNING("nsPrefBranch::SetComplexValue - Unsupported interface type");
   return NS_NOINTERFACE;