diff --git a/firefox.spec b/firefox.spec
index 988c86a..76c464e 100644
--- a/firefox.spec
+++ b/firefox.spec
@@ -52,7 +52,8 @@ Patch12:	mozilla-42-kde.patch
 #Patch13:	mozilla-kde-background.patch
 Patch34:	xulrunner_nojit.patch
 Patch35:	firefox-37-build-with-time-independent-uuids.patch
-Patch36:    firefox-38.0-enable-NTLMv1.patch
+Patch36:	firefox-38.0-enable-NTLMv1.patch
+Patch42:	mozilla-42.0-libproxy.patch
 
 # Fedora specific patches
 # Unable to install addons from https pages
@@ -183,6 +184,7 @@ Files and macros mainly for building Firefox extensions.
 %endif
 %patch35 -p1
 %patch36 -p1
+%patch42 -p1
 
 # Fedora patches
 %patch204 -p2 -b .966424
diff --git a/mozilla-42.0-libproxy.patch b/mozilla-42.0-libproxy.patch
new file mode 100644
index 0000000..98758da
--- /dev/null
+++ b/mozilla-42.0-libproxy.patch
@@ -0,0 +1,26 @@
+# HG changeset patch
+# User Wolfgang Rosenauer <wr@rosenauer.org>
+# Parent  95b421ca30846be2b5d7230d72263e6dff042d0b
+Bug 1220399 - building with libproxy support fails
+
+diff --git a/toolkit/system/unixproxy/nsLibProxySettings.cpp b/toolkit/system/unixproxy/nsLibProxySettings.cpp
+--- a/toolkit/system/unixproxy/nsLibProxySettings.cpp
++++ b/toolkit/system/unixproxy/nsLibProxySettings.cpp
+@@ -2,16 +2,17 @@
+ /* 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/. */
+ 
+ #include "nsISystemProxySettings.h"
+ #include "mozilla/ModuleUtils.h"
+ #include "nsIServiceManager.h"
+ #include "nsIURI.h"
++#include "nsNetCID.h"
+ #include "nsString.h"
+ #include "nsCOMPtr.h"
+ #include "nspr.h"
+ 
+ extern "C" {
+ #include <proxy.h>
+ }
+