I'm trying simple modify an [extension example](https://github.com/mdn/webextensions-examples/tree/master/native-messaging) to run firefox,but I get a message prompt :

`Firefox is already running,but is no responding. To open a new new window, you must firest close the existing Firefox process, or restart your system.`

```
#!/usr/bin/env python3

import sys
import json
import struct
import subprocess

try:
    # Python 3.x version
    # Read a message from stdin and decode it.
    def getMessage():
        rawLength = sys.stdin.buffer.read(4)
        if len(rawLength) == 0:
            sys.exit(0)
        messageLength = struct.unpack('@I', rawLength)[0]
        message = sys.stdin.buffer.read(messageLength).decode('utf-8')
        return json.loads(message)

    # Encode a message for transmission,
    # given its content.
    def encodeMessage(messageContent):
        encodedContent = json.dumps(messageContent).encode('utf-8')
        encodedLength = struct.pack('@I', len(encodedContent))
        return {'length': encodedLength, 'content': encodedContent}

    # Send an encoded message to stdout
    def sendMessage(encodedMessage):
        sys.stdout.buffer.write(encodedMessage['length'])
        sys.stdout.buffer.write(encodedMessage['content'])
        sys.stdout.buffer.flush()

    while True:
        receivedMessage = getMessage()
        if receivedMessage == "ping":
            run_result=subprocess.run('firefox -P firefox_word ',shell=True,stdout=subprocess.PIPE)
            sendMessage(encodeMessage("pong3"))
except AttributeError:
    pass

```

My purpose is open a local html file by my extension or native app of my extension.