Hi!

In the Dutch OTRS queue we received a complaint about "moving" tabs on the Dutch Wikipedia. (#2020060110004991)
The reader emailed a little movie of what happens, see https://drive.google.com/file/d/1U6-GfHpIWdRG8kMNU8eCyKXi9zOip5-u/view?usp=sharing

She reads Wikipedia on a Windows laptop and is not logged-in.
What is causing this problem, and how to solve this?