diff --git a/python/mozbuild/mozpack/manifests.py b/python/mozbuild/mozpack/manifests.py
index f5078443895..67cb7fc281a 100644
--- a/python/mozbuild/mozpack/manifests.py
+++ b/python/mozbuild/mozpack/manifests.py
@@ -115,7 +115,7 @@ class InstallManifest(object):
         self._source_files = set()
 
         if path or fileobj:
-            with _auto_fileobj(path, fileobj, 'rb') as fh:
+            with _auto_fileobj(path, fileobj, 'r') as fh:
                 self._source_files.add(fh.name)
                 self._load_from_fileobj(fh)
 
@@ -174,7 +174,7 @@ class InstallManifest(object):
                 dest, content = fields[1:]
 
                 self.add_content(
-                    self._decode_field_entry(content).encode('utf-8'), dest)
+                    self._decode_field_entry(content), dest)
                 continue
 
             # Don't fail for non-actionable items, allowing
@@ -236,7 +236,7 @@ class InstallManifest(object):
 
         It is an error if both are specified.
         """
-        with _auto_fileobj(path, fileobj, 'wb') as fh:
+        with _auto_fileobj(path, fileobj, 'w') as fh:
             fh.write('%d\n' % self.CURRENT_VERSION)
 
             for dest in sorted(self._dests):
@@ -244,8 +244,7 @@ class InstallManifest(object):
 
                 parts = ['%d' % entry[0], dest]
                 parts.extend(entry[1:])
-                fh.write('%s\n' % self.FIELD_SEPARATOR.join(
-                    p.encode('utf-8') for p in parts))
+                fh.write('%s\n' % self.FIELD_SEPARATOR.join(parts))
 
     def add_symlink(self, source, dest):
         """Add a symlink to this manifest.
@@ -391,7 +390,7 @@ class InstallManifest(object):
             if install_type == self.CONTENT:
                 # GeneratedFile expect the buffer interface, which the unicode
                 # type doesn't have, so encode to a str.
-                content = self._decode_field_entry(entry[1]).encode('utf-8')
+                content = self._decode_field_entry(entry[1])
                 registry.add(dest, GeneratedFile(content))
                 continue