diff -up xulrunner-20.0/mozilla-release/media/webrtc/trunk/tools/gyp/pylib/gyp/generator/mozmake.py.rhbz-304121 xulrunner-20.0/mozilla-release/media/webrtc/trunk/tools/gyp/pylib/gyp/generator/mozmake.py
--- xulrunner-20.0/mozilla-release/media/webrtc/trunk/tools/gyp/pylib/gyp/generator/mozmake.py.rhbz-304121	2013-03-26 23:17:58.000000000 +0100
+++ xulrunner-20.0/mozilla-release/media/webrtc/trunk/tools/gyp/pylib/gyp/generator/mozmake.py	2013-04-01 11:11:56.938411785 +0200
@@ -377,7 +377,7 @@ 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,
                   self.common_mk_path)
     return True