SeleniumHQ/selenium · error · WebDriverException

Please pass in a Boolean to this call

Error message

Please pass in a Boolean to this call

What it means

Raised by the deprecated FirefoxProfile.accept_untrusted_certs setter when the assigned value is not a Python bool. The property is deprecated and the untrusted-cert behavior has moved to the Firefox Options class. The library enforces strict bool typing so that the preference is never silently coerced into a non-boolean value that Firefox would misinterpret.

Source

Thrown at py/selenium/webdriver/firefox/firefox_profile.py:132

        try:
            port = int(port)
            if port < 1 or port > 65535:
                raise WebDriverException("Port number must be in the range 1..65535")
        except (ValueError, TypeError):
            raise WebDriverException("Port needs to be an integer")
        self._port = port
        self.set_preference("webdriver_firefox_port", self._port)

    @property
    @deprecated("Allowing untrusted certs is toggled in the Options class")
    def accept_untrusted_certs(self):
        return self._desired_preferences["webdriver_accept_untrusted_certs"]

    @accept_untrusted_certs.setter
    @deprecated("Allowing untrusted certs is toggled in the Options class")
    def accept_untrusted_certs(self, value) -> None:
        if not isinstance(value, bool):
            raise WebDriverException("Please pass in a Boolean to this call")
        self.set_preference("webdriver_accept_untrusted_certs", value)

    @property
    @deprecated("Allowing untrusted certs is toggled in the Options class")
    def assume_untrusted_cert_issuer(self):
        return self._desired_preferences["webdriver_assume_untrusted_issuer"]

    @assume_untrusted_cert_issuer.setter
    @deprecated("Allowing untrusted certs is toggled in the Options class")
    def assume_untrusted_cert_issuer(self, value) -> None:
        if not isinstance(value, bool):
            raise WebDriverException("Please pass in a Boolean to this call")

        self.set_preference("webdriver_assume_untrusted_issuer", value)

    @property
    def encoded(self) -> str:
        """Update preferences and create a zipped, base64-encoded profile directory string."""

View on GitHub (pinned to aa36b38e69)

Solutions

1. Pass a literal Python bool: profile.accept_untrusted_certs = True
2. If your value comes from config/env, convert explicitly with bool() or parse 'true'/'false' strings before assignment
3. Stop using the deprecated property and set the option on the Options class instead

Example fix

// before
profile.accept_untrusted_certs = 'true'

// after
profile.accept_untrusted_certs = True

value = 'true'
if not isinstance(value, bool):
    value = str(value).lower() in ('true', '1')
profile.accept_untrusted_certs = value

def is_bool(v) -> bool:
    return isinstance(v, bool)

from selenium.common.exceptions import WebDriverException
try:
    profile.accept_untrusted_certs = config_value
except WebDriverException:
    profile.accept_untrusted_certs = bool(config_value)

When it happens

Trigger: Assigning profile.accept_untrusted_certs = 1, profile.accept_untrusted_certs = 'true', or profile.accept_untrusted_certs = None triggers the WebDriverException. Only Python True/False are accepted.

Common situations: Developers migrating from older Selenium versions where string 'true'/'false' or integer 0/1 were tolerated. Users copy-pasting YAML or JSON config values that arrive as strings rather than native booleans.

Related errors

• Port needs to be an integer
• Port number must be in the range 1..65535
• Autodetect proxy value needs to be a boolean
• Add-on path does not exist: {addon_path}
• Add-on path is neither an XPI nor a directory: {addon_path}

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/d8659756a999cd63. Report an issue: GitHub.