Not able to set proxy in selenium Python

I have the following bit of code:

from selenium import webdriver
from selenium.webdriver import Firefox
from selenium.webdriver.common.keys import Keys
from selenium.webdriver import ActionChains

from selenium.webdriver.common.proxy import Proxy, ProxyType

proxy = Proxy({
    'proxyType': ProxyType.MANUAL,
    'httpProxy': '192.156.1.1:33',
    'ftpProxy': '192.156.1.1:33',
    'sslProxy': '192.156.1.1:33',
    'noProxy': '' # set this value as desired
    })
url = 'http://www.expressvpn.com/what-is-my-ip'
driver_path = 'C:\\Users\\user\\geckodriver.exe'

browser = Firefox(executable_path = driver_path, proxy = proxy)
browser.get(url)

For some reason everytime i check the ip, it is showing my true IP and not the proxy IP. Why is it doing that and could you please advise how this can be accomplished? Is there some problem with the code?

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