I use this web page to show the scroll problem in Firefox for Android.

This web page comes from an article of the site "lci.fr". I downloaded this page saved in the wayback machine thanks to this software : https://github.com/hartator/wayback-machine-downloader, at this URL : https://web.archive.org/web/20161017144432/http://www.lci.fr/sante/le-premier-souffle-a-ete-une-delivrance-adeline-raconte-sa-greffe-des-poumons-2008090.html

In this web page, the navigation bar auto-hides when you scroll down and reappears when you scroll up, so the problem clearly appears. Comparison video between Chrome and Firefox here : https://www.youtube.com/watch?v=LRCd-xFJrZY

In the code of this web page, you will see a lot of useless code. I removed some lines, but I don't know well JavaScript, so I can do no more, sorry.