[🐛 Bug]: Message: binary is not a Firefox executable

[arghorashy]

Description

I have a python script I have working on one computer, but when I try to run it on my server I get the following error:

    self.driver = webdriver.Firefox(service=service, options=options)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/firefox/webdriver.py", line 71, in __init__
    super().__init__(command_executor=executor, options=options)
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 241, in __init__
    self.start_session(capabilities)
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 329, in start_session
    response = self.execute(Command.NEW_SESSION, caps)["value"]
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 384, in execute
    self.error_handler.check_response(response)
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/errorhandler.py", line 232, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.InvalidArgumentException: Message: binary is not a Firefox executable

Here is the code I'm running:

from selenium import webdriver
from selenium.webdriver.firefox.options import Options
from selenium.webdriver.firefox.firefox_binary import FirefoxBinary
import selenium.webdriver.firefox.service as FirefoxService

options = Options()
service = FirefoxService.Service(executable_path='/snap/bin/geckodriver')
options.binary_location = "/usr/bin/firefox"
webdriver.Firefox(service=service, options=options)

On my computer where this worked, I didn't need to specify locations for geckodriver or firefox. If I get rid of the arguments to webdriver.Firefox, I get the same result, by the way, so I'm not sure they're doing anything...

Here is some relevant version info for the original computer where this worked:

• OS: Linux Mint 22.1
• Python v3.12.3
• Selenium v4.27.1
• Firefox v135.0.1
• Gecko - interestingly which geckodriver returns nothing

Here is some version information for the server where I am encountering this issue:

• OS: Ubuntu 22.04.5 LTS
• Python v3.12.10
• Selenium v4.31.0
• Firefox v138.0
• Gecko v0.36.0

Reproducible Code

from selenium import webdriver
from selenium.webdriver.firefox.options import Options
from selenium.webdriver.firefox.firefox_binary import FirefoxBinary
import selenium.webdriver.firefox.service as FirefoxService

options = Options()
service = FirefoxService.Service(executable_path='/snap/bin/geckodriver')
options.binary_location = "/usr/bin/firefox"
webdriver.Firefox(service=service, options=options)

Debugging Logs

self.driver = webdriver.Firefox(service=service, options=options)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/firefox/webdriver.py", line 71, in __init__
    super().__init__(command_executor=executor, options=options)
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 241, in __init__
    self.start_session(capabilities)
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 329, in start_session
    response = self.execute(Command.NEW_SESSION, caps)["value"]
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 384, in execute
    self.error_handler.check_response(response)
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/errorhandler.py", line 232, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.InvalidArgumentException: Message: binary is not a Firefox executable

[selenium-ci]

@arghorashy, 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]

It looks like you are running the Snap version of geckodriver, but a non-Snap version of Firefox? That might be problematic.

If I get rid of the arguments to webdriver.Firefox, I get the same result

That should work (it will download the latest Firefox and geckodriver)

Can you please do the following:

• enable DEBUG level logging: https://www.selenium.dev/documentation/webdriver/troubleshooting/logging/
• Try again using webdriver.Firefox() with no args
• paste the log output here

[arghorashy]

Thanks for your reply. Per your instructions, I ran this:

import logging
logger = logging.getLogger('selenium')
logger.setLevel(logging.DEBUG)
log_path = './log'
handler = logging.FileHandler(log_path)
logger.addHandler(handler)

from selenium import webdriver
webdriver.Firefox()

In STDOUT I got this:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/firefox/webdriver.py", line 71, in __init__
    super().__init__(command_executor=executor, options=options)
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 250, in __init__
    self.start_session(capabilities)
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 342, in start_session
    response = self.execute(Command.NEW_SESSION, caps)["value"]
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/webdriver.py", line 429, in execute
    self.error_handler.check_response(response)
  File ".venv/lib/python3.12/site-packages/selenium/webdriver/remote/errorhandler.py", line 232, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.InvalidArgumentException: Message: binary is not a Firefox executable

In my log file I got this output:

Selenium Manager binary found at: .venv/lib/python3.12/site-packages/selenium/webdriver/common/linux/selenium-manager
Executing process: .venv/lib/python3.12/site-packages/selenium/webdriver/common/linux/selenium-manager --browser firefox --debug --language-binding python --output json
Found geckodriver 0.36.0 in PATH: /snap/bin/geckodriver
firefox detected at /usr/bin/firefox
Running command: /usr/bin/firefox -v
Output: "Mozilla Firefox 138.0"
Detected browser: firefox 138.0
Required driver: geckodriver 0.36.0
Driver path: /snap/bin/geckodriver
Browser path: /usr/bin/firefox
Started executable: `/snap/bin/geckodriver` in a child process with pid: 5691 using 0 to output -3
POST http://localhost:55333/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': 3}}}}}
Remote response: status=400 | data={"value":{"error":"invalid argument","message":"binary is not a Firefox executable","stacktrace":""}} | headers=HTTPHeaderDict({'content-type': 'application/json; charset=utf-8', 'cache-control': 'no-cache', 'content-length': '101', 'date': 'Wed, 30 Apr 2025 20:59:32 GMT'})
Finished Request

[selenium-ci]

We need more information about this issue in order to troubleshoot.

Please turn on logging and re-run your code. Information on how to adjust logs for your language can be found in our
Troubleshooting documentation.

[cgoldberg]

@arghorashy
The log shows it is still using your system browser/driver rather than downloading the latest. I'm not sure why that is happening.

Can you try running your code with the SE_FORCE_BROWSER_DOWNLOAD environment variables set to true? So in your shell, just run export SE_FORCE_BROWSER_DOWNLOAD=true, then run your code.

@bonigarcia Do you know what is going on here? Based on the code/log shown in #15683 (comment) , shouldn't Selenium Manager not be using the system driver/browser?