public static class CustomWebDriverProvider implements WebDriverProvider {
    @Override
    public WebDriver createDriver(DesiredCapabilities capabilities) {
      FirefoxProfile profile = new FirefoxProfile(new File("/home/test/MozzillaProf/"));
      FirefoxOptions firefoxOptions = new FirefoxOptions()
        .setProfile(profile)
        .setAcceptInsecureCerts(true)
        .addPreference("general.useragent.override", "some UA string")
        .merge(capabilities);

      return new FirefoxDriver(firefoxOptions);
    }
  }

Element not found {[unknown locator]}
Expected: visible
Screenshot: file:/C:/work/selenide/build/reports/tests/1572705019957.0.png
Page source: file:/C:/work/selenide/build/reports/tests/1572705019957.0.html
Timeout: 4 s.
Caused by: NoSuchElementException: Cannot locate an element using [unknown locator]