The newly introduced footer is extending in the https://stackexchange.com site in mobile web view.
Screenshot for reference:
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The Stack Exchange Portal is a desktop site. It does not have a mobile view by far.
We don't officially support the weird things mobile browsers do to the page.
Using the desktop view on mobile, you're bound to find oddities as mobile devices use very different methods of rendering.
Let's wait for SE to develop a mobile portal.