[🐛 Bug]: `webdriver.Firefox()` fails with `'status': [13, 'unknown error']`

[sci-42ver]

Description

I follow the doc https://selenium-python.readthedocs.io/getting-started.html#simple-usage and expects to work, but it failed with selenium.common.exceptions.WebDriverException: Message: without saying more about that Message.

System info:

• OS: Arch Linux 6.13.6-arch1-1
• Python: 3.13.2
• Firefox: 138.0.4

Backtrace:

Traceback (most recent call last):
  File "/home/hervey_arch/py_crawler_qq/tmp_debug.py", line 10, in <module>
    from selenium import webdriver;driver = webdriver.Firefox()
                                            ~~~~~~~~~~~~~~~~~^^
  File "/home/hervey_arch/main-env/lib/python3.13/site-packages/selenium/webdriver/firefox/webdriver.py", line 71, in __init__
    super().__init__(command_executor=executor, options=options)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/hervey_arch/main-env/lib/python3.13/site-packages/selenium/webdriver/remote/webdriver.py", line 260, in __init__
    self.start_session(capabilities)
    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
  File "/home/hervey_arch/main-env/lib/python3.13/site-packages/selenium/webdriver/remote/webdriver.py", line 357, in start_session
    response = self.execute(Command.NEW_SESSION, caps)["value"]
               ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/hervey_arch/main-env/lib/python3.13/site-packages/selenium/webdriver/remote/webdriver.py", line 448, in execute
    self.error_handler.check_response(response)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "/home/hervey_arch/main-env/lib/python3.13/site-packages/selenium/webdriver/remote/errorhandler.py", line 196, in check_response
    raise exception_class(value)
selenium.common.exceptions.WebDriverException: Message: 

I use pdb to find the problem, the above response is {'status': [13, 'unknown error'], 'value': ''}, caps is same as what the log shows, capabilities is {'browserName': 'firefox', 'acceptInsecureCerts': True, 'moz:debuggerAddress': True, 'pageLoadStrategy': <PageLoadStrategy.normal: 'normal'>, 'browserVersion': None, 'moz:firefoxOptions': {'binary': '/usr/bin/firefox', 'prefs': {'remote.active-protocols': 1}}} and the rest are the default:

(Pdb) p executor
<selenium.webdriver.firefox.remote_connection.FirefoxRemoteConnection object at 0x74b282e057f0>
(Pdb) p options
<selenium.webdriver.firefox.options.Options object at 0x74b282e05160>

Reproducible Code

from selenium import webdriver;driver = webdriver.Firefox()

Debugging Logs

Selenium Manager binary found at: /home/hervey_arch/main-env/lib/python3.13/site-packages/selenium/webdriver/common/linux/selenium-manager
Executing process: /home/hervey_arch/main-env/lib/python3.13/site-packages/selenium/webdriver/common/linux/selenium-manager --browser firefox --debug --language-binding python --output json
Found geckodriver 0.36.0 in PATH: /usr/bin/geckodriver
firefox detected at /usr/bin/firefox
Running command: /usr/bin/firefox -v
Output: "Mozilla Firefox 138.0.4"
Detected browser: firefox 138.0.4
Required driver: geckodriver 0.36.0
Driver path: /usr/bin/geckodriver
Browser path: /usr/bin/firefox
Started executable: `/usr/bin/geckodriver` in a child process with pid: 53733 using 0 to output -3
POST http://localhost:38413/session {'capabilities': {'firstMatch': [{}], 'alwaysMatch': {'browserName': 'firefox', 'acceptInsecureCerts': True, 'moz:debuggerAddress': True, 'pageLoadStrategy': <PageLoadStrategy.normal: 'normal'>, 'browserVersion': None, 'moz:firefoxOptions': {'binary': '/usr/bin/firefox', 'prefs': {'remote.active-protocols': 1}}}}}
Remote response: status=503 | data= | headers=HTTPHeaderDict({'Connection': 'close', 'Proxy-Connection': 'close', 'Content-Length': '0'})
Finished Request

[selenium-ci]

@sci-42ver, thank you for creating this issue. We will troubleshoot it as soon as we can.

Selenium Triage Team: remember to follow the Triage Guide

[cgoldberg]

@sci-42ver What version of Selenium are you using, and where did you install it from?

It looks like you have geckodriver installed already. Where did you install it from? You might have better luck removing it and letting Selenium install the correct version for you (via selenium-manager).

[sci-42ver]

@sci-42ver What version of Selenium are you using

I use the latest 4.32.0 which can be also checked with pip (see the following).

I added that in the original post but that is removed by the github-actions. You can check that in the Edits.

and where did you install it from?

I use pip.

$ source ~/main-env/bin/activate    
(main-env)  $ pip show Selenium
Name: selenium
Version: 4.32.0
Summary: Official Python bindings for Selenium WebDriver
Home-page: https://www.selenium.dev
Author: 
Author-email: 
License: Apache 2.0
Location: /home/hervey_arch/main-env/lib/python3.13/site-packages
Requires: certifi, trio, trio-websocket, typing_extensions, urllib3, websocket-client
Required-by: helium
(main-env)  $ pip --version
pip 24.3.1 from /home/hervey_arch/main-env/lib/python3.13/site-packages/pip (python 3.13)

It looks like you have geckodriver installed already. Where did you install it from?

I installed geckodriver by yay -S geckodriver. You can check https://archlinux.org/packages/extra/x86_64/geckodriver/ for details.

You might have better luck removing it and letting Selenium install the correct version for you (via selenium-manager).

I tried selenium-manager first before using yay but the issue is still there.

[cgoldberg]

Can you try starting firefox and geckodriver from the command line and verify both launch with no errors?

[sci-42ver]

Can you try starting firefox and geckodriver from the command line and verify both launch with no errors?

Yes and the latter has

$ geckodriver
1748336598624   geckodriver     INFO    Listening on 127.0.0.1:4444

which seems to be expected mozilla/geckodriver#510 (comment).