--- a/python/mozbuild/mozpack/chrome/manifest.py.orig	1980-01-01 18:59:51.000000000 -0500
+++ b/python/mozbuild/mozpack/chrome/manifest.py	2019-11-16 22:14:47.497320339 -0500
@@ -368,4 +368,5 @@
     Return whether the given path is that of a manifest file.
     '''
     return path.endswith('.manifest') and not path.endswith('.CRT.manifest') \
-        and not path.endswith('.exe.manifest')
+        and not path.endswith('.exe.manifest') and not path.endswith('cose.manifest')
+