[Django]-Why is Django cms sitemap url not matching in all browsers?

for all those who are still wondering what that “/” means than simply update the url

from

url(r'^sitemap\.xml$', 'django.contrib.sitemaps.views.sitemap',
        {'sitemaps': {'cmspages': CMSSitemap}}),

to

url(r'^sitemap\.xml/$', 'django.contrib.sitemaps.views.sitemap',
        {'sitemaps': {'cmspages': CMSSitemap}}),

I can’t believe I spent so much time not noticing that the final / was the cause of the problem.
I’ll leave this post here just in case it saves someone else some time …