--- a/testing/web-platform/mach_commands.py
+++ b/testing/web-platform/mach_commands.py
@@ -218,25 +218,28 @@ testing/web-platform/tests for tests tha
             editor = kwargs["editor"]
         elif "VISUAL" in os.environ:
             editor = os.environ["VISUAL"]
         elif "EDITOR" in os.environ:
             editor = os.environ["EDITOR"]
         else:
             editor = None
 
+        proc = None
         if editor:
             proc = subprocess.Popen("%s %s" % (editor, path), shell=True)
 
         if not kwargs["no_run"]:
             p = create_parser_wpt()
             wpt_kwargs = vars(p.parse_args(["--manifest-update", path]))
             context.commands.dispatch("web-platform-tests", context, **wpt_kwargs)
 
-        proc.wait()
+        if proc:
+            proc.wait()
+
 
 def create_parser_wpt():
     from wptrunner import wptcommandline
     return wptcommandline.create_parser(["firefox"])
 
 def create_parser_update():
     from update import updatecommandline
     return updatecommandline.create_parser()