TypeError: Object of type 'Checkbox' is not JSON serializable

[AlexanderGrigoryev]

This code work in Google Chrome and raise TypeError in Mozilla Firefox:

from selenium.webdriver.remote.webelement import WebElement

class Clickable(WebElement):
      """ Clickable class from webium """
      pass

class Checkbox(Clickable):
      """ Checkbox class from webium """
      pass

This code work in Google Chrome and in Mozilla Firefox:

from selenium.webdriver.firefox.webelement import FirefoxWebElement as WebElement

class Clickable(WebElement):
      """ Clickable class from webium """
      pass

class Checkbox(WebElement):
      """ Checkbox class from webium """
      pass

Versions of tools:

webium 1.2.1           Google Chrome 68.0.3440.84 (64-бит)        Mozilla Firefox 61.0.1 (64-бит)
selenium 3.14.0        chromedriver 2.41 (32-бит)                 geckodriver 0.21.0 (64-бит)