This should be fixed by adding space at bottom of page so that the footer can be scrolled past. The height of sticky element should equal extra bottom padding
Test should hold true for any browser in the list https://www.mediawiki.org/wiki/Reading/Web/QA_device_and_browsers_list
Visit https://en.m.wikipedia.beta.wmflabs.org/wiki/Special:MobileDiff/265240?mobileaction=beta and make sure that the page footer is not covered by the user information. When you scroll down the page you should be able to see the whole page footer and then the user information box should appear.
Basically, it should look like this:
and not like this: