How to use Mozilla's YouTube downloader?

Hey guys,

I am working on a Python project which will enable to watch movies on YouTube easily.

I have added 'YouTube Video Downloader' as an add-on to my Mozilla we browser. Now, everytime I enter a list of URLs containing the movie I want to watch in parts, the program should open the URL, and use the add-on to download the video. How is it possible? I have some basic code here, but have no clue on how to use the add-on

import time
import urllib2
import os

print("Welcome.")
n=input("How many parts are there of the video you want to watch? ")
print("Please wait...")

time.sleep(3)
os.system('cls')

s=[]

for x in range(n):
    s.append(raw_input("Enter URL: "))

os.system('cls')

for x in s:
    urllib.urlopen(x)

Thanks