Steps to reproduce: start with cold cache, click on thumbnail before scripts are fully loaded, press Esc when screen goes black. Loading stops, and user is stuck with a black screen until they reload.
This results somehow from the interaction of head.js and bootstrap.js - I cannot reproduce it by clicking when the page has finished loading.
Given how hard it is to trigger this bug, might be fine to just leave it.
Version: unspecified
Severity: minor
I think this only happens when clicking on a thumbnail before the page is fully loaded (domready), just that the scrips haven't finished loading does not trigger it.
Mass-removing the Multimedia tag from MediaViewer tasks, as this is now being worked on by the Reading department, not Editing's Multimedia team.
I can't reproduce. It may have been fixed by https://gerrit.wikimedia.org/r/c/mediawiki/extensions/MultimediaViewer/+/910522, or maybe some earlier change.