diff -up firefox-18.0/mozilla-release/media/webrtc/trunk/Makefile.old firefox-18.0/mozilla-release/media/webrtc/trunk/Makefile
diff -up firefox-18.0/mozilla-release/media/webrtc/trunk/tools/gyp/pylib/gyp/generator/mozmake.py.old firefox-18.0/mozilla-release/media/webrtc/trunk/tools/gyp/pylib/gyp/generator/mozmake.py
--- firefox-18.0/mozilla-release/media/webrtc/trunk/tools/gyp/pylib/gyp/generator/mozmake.py.old	2013-01-05 00:44:41.000000000 +0100
+++ firefox-18.0/mozilla-release/media/webrtc/trunk/tools/gyp/pylib/gyp/generator/mozmake.py	2013-01-10 14:48:58.418321640 +0100
@@ -376,7 +376,7 @@ class MakefileGenerator(object):
     WriteMakefile(output_file, data, build_file, depth, top,
                   # we set srcdir up one directory, since the subdir
                   # doesn't actually exist in the source directory
-                  swapslashes(os.path.join(top, self.relative_srcdir, os.path.split(rel_path)[0])),
+                  swapslashes(os.path.normpath(os.path.join(top, self.relative_srcdir, os.path.split(rel_path)[0]))),
                   self.relative_srcdir)
     return True