The script at
(or https://www.wikidata.org/w/extensions/Wikibase/view/resources/jquery/wikibase/jquery.wikibase.entityview.js?da0f6 )
has the line
$.expr[ ':' ][ $.wikibase.entityview.prototype.widgetFullName ]
which causes the warning
JQMIGRATE: jQuery.expr[':'] is deprecated; use jQuery.expr.pseudos
in the console when visiting
https://www.wikidata.org/wiki/Special:Watchlist?debug=1