http://www.mediawiki.org/wiki/Extension:SyntaxHighlight_GeSHi#More_Usage claims that the optional GeSHi line numbering implicitly enables line wrapping, giving an example, where this obviously does NOT work at the moment. The explicit addition of enclose="div" by me today had the desired effect on an intentionally long line. However, the wrapped output now shows a comment intended to be hidden.
Is this a bug in my browser (Chrome), GeSHi, MediaWiki, or in the MediaWiki extension documentation?
That's a bug in the MediaWiki extension.