Last modified: 2014-11-06 12:32:40 UTC
Here is what I found. Document is in BackCompat mode because this is at the beginning of the html: <noscript><img src="//en.wikipedia.beta.wmflabs.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" title="" width="1" height="1" style="border: none; position: absolute;" /></noscript> This causes jQuery migrate to show a warning: if ( document.compatMode === "BackCompat" ) { // jQuery has never supported or tested Quirks Mode migrateWarn( "jQuery is not compatible with Quirks Mode" ); } migrateWarn() uses mw.track, which is not yet defined, causing JavaScript error.
I filed bug 73080 for the last part. Our real problem is however the HTML code from CentralAuth appearing in a wrong place.