Fork off webbrowser call in case it fails to return

calls to webbrowser.open do not return for command-line browser, so run it in a fork

nikola/plugins/command/serve.py

@@ -141,7 +141,10 @@ def _execute(self, options, args):
                 if sa[0] == '0.0.0.0':
                     server_url = "http://127.0.0.1:{1}/".format(*sa)
                 self.logger.info("Opening {0} in the default web browser...".format(server_url))
-                webbrowser.open(server_url)
+                pid = os.fork()
+                if pid == 0:
+                    webbrowser.open(server_url)
+                    sys.exit(0)
             if options['detach']:
                 self.detached = True
                 OurHTTPRequestHandler.quiet = True