browse.py: fix delay with multiple connections

When Firefox opens two TCP connections and sends a request over the
second connection, it is not processed until the first one is closed.
Use a threaded server to solve this issue. Tested with Python 2.7.15 and
3.6.5. (Also tested with 2.6, but that failed due to lack of argparse.)

Link: https://bugs.python.org/issue31639
1 file changed