Proxies does not work in Selenium (Firefox)

Question

The second day I try to find a working solution, but nothing comes out, proxies doesn't work. Please help me, I would be very grateful to you. From documentation -

    PROXY = "<100.200.300.400:5000>"
    webdriver.DesiredCapabilities.FIREFOX['proxy'] = {
"httpProxy": PROXY,
"ftpProxy": PROXY,
"sslProxy": PROXY,
"proxyType": "MANUAL",

}

    driver = webdriver.Firefox()