We run a Mediawiki installation on Ubuntu Server 20.04 x86_64. The server is fully patched. We upgrade from Mediawiki 1.36 to Mediawiki 1.36.1 today.
It looks like the Vector skin no longer works as expected. It was working fine until we upgraded today. After restarting the server we get this infamous warning:
Deprecated: Use of BaseTemplate::getFooterIcons was deprecated in MediaWiki 1.35. [Called from VectorTemplate::getFooterData in /var/www/html/w/skins/Vector/includes/VectorTemplate.php at line 223] in /var/www/html/w/includes/debug/MWDebug.php on line 376
It looks like the warning breaks the CSS. Previously skins that witnessed the warning just printed the warning but applied the skin's formatting. Now it does not apply the formatting.
The browser were are seeing the issue under is Firefox 89.0.1 (64-bit).
I also question the wisdom of running debug code in production. We don't run debug developer gear on our server. All this developer debug code does is increase attack surface and cause problems. Mediawiki should consider removing it from release or production code that is released to the world.