def start(self, captureNetworkTraffic=False):
    l = [self.browserStartCommand, self.browserURL, self.extensionJs]
if captureNetworkTraffic:
    l.append('captureNetworkTraffic=true')
result = self.get_string('getNewBrowserSession', l)
Selenium-rc: как вы используете CaptureNetworkTraffic в python