Selenium “Unable to find a matching set of capabilities” despite driver being in /usr/local/bin

Question

I'm trying to follow a tutorial about Selenium, http://selenium-python.readthedocs.io/getting-started.html. I've downloaded the latest version of the geckodriver and copied it to /usr/local/bin. However, when I try

from selenium import webdriver

driver = webdriver.Firefox()

I get the following error message:

Traceback (most recent call last):

  File "/Users/kurtpeek/Documents/Scratch/selenium_getting_started.py", line 4, in <module>

    driver = webdriver.Firefox()

  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/selenium/webdriver/firefox/webdriver.py", line 152, in __init__

    keep_alive=True)

  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.py", line 98, in __init__

    self.start_session(desired_capabilities, browser_profile)

  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.py", line 188, in start_session

    response = self.execute(Command.NEW_SESSION, parameters)

  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.py", line 252, in execute

    self.error_handler.check_response(response)

  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/selenium/webdriver/remote/errorhandler.py", line 194, in check_response

    raise exception_class(message, screen, stacktrace)

selenium.common.exceptions.WebDriverException: Message: Unable to find a matching set of capabilities

[Finished in 1.2s with exit code 1]

From https://github.com/SeleniumHQ/selenium/issues/3884, it seems like other users are experiencing similar issues, but the Selenium team is unable to reproduce it. How can I get Selenium working with Firefox? (It does work with chromedriver and a webdriver.Chrome() instance, so I suspect this might be a bug in Selenium).

Answer 1

In my case, I have updated Firefox and Selenium. 

Updated Firefox 48 → 53

Updated to Selenium 3.4.1

I also used Homebrew to reinstall/update Geckodriver and explicitly use it as an executable for Selenium WebDriver, but it turned out that it wasn't necessary to mitigate the "Unable to find a matching set of capabilities" error.

Also, check whether you have the correct version 32/64bit for your geckodriver or not.