How do I switch to the active tab in Selenium?

We developed a Chrome extension, and I want to test our extension with Selenium. I created a test, but the problem is that our extension opens a new tab when it's installed, and I think I get an exception from the other tab. Is it possible to switch to the active tab I'm testing? Or another option is to start with the extension disabled, then login to our website and only then enable the extension. Is it possible? Here is my code:

def login_to_webapp(self):
    self.driver.get(url='http://example.com/logout')
    self.driver.maximize_window()
    self.assertEqual(first="Web Editor", second=self.driver.title)
    action = webdriver.ActionChains(driver=self.driver)
    action.move_to_element(to_element=self.driver.find_element_by_xpath(xpath="//div[@id='header_floater']/div[@class='header_menu']/button[@class='btn_header signature_menu'][text()='My signature']"))
    action.perform()
    self.driver.find_element_by_xpath(xpath="//ul[@id='signature_menu_downlist'][@class='menu_downlist']/li[text()='Log In']").click()
    self.driver.find_element_by_xpath(xpath="//form[@id='atho-form']/div[@class='input']/input[@name='useremail']").send_keys("[email]")
    self.driver.find_element_by_xpath(xpath="//form[@id='atho-form']/div[@class='input']/input[@name='password']").send_keys("[password]")
    self.driver.find_element_by_xpath(xpath="//form[@id='atho-form']/button[@type='submit'][@class='atho-button signin_button'][text()='Sign in']").click()

The test fails with ElementNotVisibleException: Message: element not visible, because in the new tab (opened by the extension) "Log In" is not visible (I think the new tab is opened only after the command self.driver.get(url='http://example.com/logout')).

Update: I found out that the exception is not related to the extra tab, it's from our website. But I closed the extra tab with this code, according to @aberna's answer:

def close_last_tab(self):
    if (len(self.driver.window_handles) == 2):
        self.driver.switch_to.window(window_name=self.driver.window_handles[-1])
        self.driver.close()
        self.driver.switch_to.window(window_name=self.driver.window_handles[0])

After closing the extra tab, I can see my tab in the video.