[🐛 Bug]: Failed to set preferences: unknown error when specify a profile.

[heckad]

What happened?

Expected Behavior -
Firefox run withprovided profile

Actual Behavior -
Firefox is not running

How can we reproduce the issue?

from selenium import webdriver
from selenium.webdriver.firefox.options import Options

firefox_options = Options()
firefox_options.add_argument("--profile D:\\path\\to\\profile\\dir")
driver = webdriver.Firefox(options=firefox_options)

Python's traceback

Traceback (most recent call last):
  File "/app/tmp/t.py", line 24, in <module>
    driver = webdriver.Firefox(options=firefox_options)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/selenium/webdriver/firefox/webdriver.py", line 71, in __init__
    super().__init__(command_executor=executor, options=options)
  File "/usr/local/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 212, in __init__
    self.start_session(capabilities)
  File "/usr/local/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 299, in start_session
    response = self.execute(Command.NEW_SESSION, caps)["value"]
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 354, in execute
    self.error_handler.check_response(response)
  File "/usr/local/lib/python3.12/site-packages/selenium/webdriver/remote/errorhandler.py", line 229, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.SessionNotCreatedException: Message: Failed to set preferences: unknown error

Relevant log output

1729892750450	geckodriver	INFO	Listening on 127.0.0.1:58119
1729892753487	webdriver::server	DEBUG	-> POST /session {"capabilities": {"firstMatch": [{}], "alwaysMatch": {"browserName": "firefox", "acceptInsecureCerts": true, ... .active-protocols": 3}, "args": ["--profile D:\\path\\to\\profile\\dir"]}}}}
1729892753487	geckodriver::capabilities	DEBUG	Trying to read firefox version from ini files
1729892753488	geckodriver::capabilities	DEBUG	Found version 131.0.3
1729892753488	webdriver::server	DEBUG	<- 500 Internal Server Error {"value":{"error":"session not created","message":"Failed to set preferences: unknown error","stacktrace":""}}

Operating System

Windows 11

Selenium version

python 3.12

What are the browser(s) and version(s) where you see this issue?

131.0.3

What are the browser driver(s) and version(s) where you see this issue?

GecoDriver 0.35.0

Are you using Selenium Grid?

No response

[github-actions]

@heckad, thank you for creating this issue. We will troubleshoot it as soon as we can.

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Thank you!

[Delta456]

The given code is incomplete.

[heckad]

No, that's really all except two imports (Updated messaged to add them and add python's traceback).

[navin772]

Hi @heckad, I was able to reproduce this issue on a Windows machine.

Interestingly, this isn't a problem on macOS; the script worked fine, and the required profile was launched.

[Delta456]

Hi @heckad! Can you try this?

from selenium import webdriver
from selenium.webdriver.firefox.options import Options

firefox_options = Options()
firefox_options.add_argument(r"--profile D:\\path\\to\\profile\\dir")
driver = webdriver.Firefox(options=firefox_options)

EDIT: This won't fix it, please ignore.

[heckad]

Yer, in row string mode you can write a path without double slashes.

[heckad]

I have the same problem on my Linux machine and in Docker too.
Reproducible dockerfile

FROM python:3.12

# Install Firefox
ARG FIREFOX_VERSION=131.0
RUN echo "deb http://deb.debian.org/debian/ unstable main contrib non-free" >> /etc/apt/sources.list.d/debian.list
RUN apt-get update -qqy \
  && apt-get -qqy --no-install-recommends install firefox \
  && rm -rf /var/lib/apt/lists/* /var/cache/apt/* \
  && wget --no-verbose -O /tmp/firefox.tar.bz2 https://download-installer.cdn.mozilla.net/pub/firefox/releases/$FIREFOX_VERSION/linux-x86_64/en-US/firefox-$FIREFOX_VERSION.tar.bz2 \
  && apt-get -y purge firefox \
  && rm -rf /opt/firefox \
  && tar -C /opt -xjf /tmp/firefox.tar.bz2 \
  && rm /tmp/firefox.tar.bz2 \
  && mv /opt/firefox /opt/firefox-$FIREFOX_VERSION \
  && ln -fs /opt/firefox-$FIREFOX_VERSION/firefox /usr/bin/firefox

RUN pip install selenium

RUN cat <<EOF > main.py
import sys
from pathlib import Path

from selenium import webdriver
from selenium.webdriver.firefox.options import Options
from selenium.webdriver.firefox.service import Service

path = Path(__file__).parent / "firefox_profile"

firefox_options = Options()
firefox_options.add_argument(f"--profile {path}")
firefox_options.add_argument("--headless")
firefox_options.log.level = "trace"
driver = webdriver.Firefox(options=firefox_options, service=Service(log_output=sys.stdout))
driver.get("https://google.com")
driver.quit()
EOF

CMD ["python", "main.py"]