import webbrowser
firefox = webbrowser.get('firefox')
f = open ('C:\\Users\\test\\Desktop\\urls.txt','r')
data = f.read()
for urls in data.split('\n'):
    firefox.open_new_tab(urls)


  File "C:\PYTHON32\LIB\webbrowser.py", line 53, in get
    raise Error("could not locate runnable browser")
webbrowser.Error: could not locate runnable browser