SessionNotCreatedException: Message: Expected browser binary location, but unable to find binary in default location, no 'moz:firefoxOptions.binary'

Question

When I try to create a Firefox instance in Selenium, I get the following error:

Message: Expected browser binary location, but unable to find binary in default location, no 'moz:firefoxOptions.binary' capability provided, and no binary flag set on the command line 

I'm running on Ubuntu 20.04
Any suggestions would be appreciated .

browser = webdriver.Firefox()

Traceback (most recent call last):
  File "key.py", line 10, in <module>
    browser = webdriver.Firefox()
  File "/usr/local/lib/python3.8/dist-packages/selenium/webdriver/firefox/webdriver.py", line 170, in __init__
    RemoteWebDriver.__init__(
  File "/usr/local/lib/python3.8/dist-packages/selenium/webdriver/remote/webdriver.py", line 157, in __init__
    self.start_session(capabilities, browser_profile)
  File "/usr/local/lib/python3.8/dist-packages/selenium/webdriver/remote/webdriver.py", line 252, in start_session
    response = self.execute(Command.NEW_SESSION, parameters)
  File "/usr/local/lib/python3.8/dist-packages/selenium/webdriver/remote/webdriver.py", line 321, in execute
    self.error_handler.check_response(response)
  File "/usr/local/lib/python3.8/dist-packages/selenium/webdriver/remote/errorhandler.py", line 242, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.SessionNotCreatedException: Message: Expected browser binary location, but unable to find binary in default location, no 'moz:firefoxOptions.binary' capability provided, and no binary flag set on the command line

Solution

This error message...

selenium.common.exceptions.SessionNotCreatedException: Message: Expected browser binary location, but unable to find binary in default location, no 'moz:firefoxOptions.binary' capability provided, and no binary flag set on the command line

...implies that the GeckoDriver was unable to locate the firefox binary while trying to initiate/spawn a new Browsing Context i.e. Firefox Browser session.

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Reason

The probable reason for this error can be either of the following:

• Firefox isn't installed in your system.
• Firefox isn't installed in the default location within your system.

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Solution

The possible solutions are:

• If Firefox isn't installed in your system, you need to install it before executing your tests.

• If Firefox is installed at a customized location, you need to pass the absolute path of the firefox binary as follows through an Options() instance:

  from selenium import webdriver
  from selenium.webdriver.firefox.options import Options
  
  options = Options()
  options.binary_location = r"C:/location/to/Firefox/Binary/firefox.exe"
  driver = webdriver.Firefox(options=options, executable_path="C:/location/to/geckodriver.exe")
  driver.get('http://google.com/')
  

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References

You can find a couple of relevant detailed discussion in:

• InvalidArgumentException: Message: binary is not a Firefox executable error using GeckoDriver Firefox Selenium and Python
• Expected browser binary location, but unable to find binary in default location, no 'moz:firefoxOptions.binary' capability provided
• Expected browser binary location, but unable to find binary in default location, no 'moz:firefoxOptions.binary' capability provided using GeckoDriver