The web is a complex platform, so it's definitely not hard to wind up using some feature that performs well in one browser but poorly in another. I don't know that it necessarily reflects badly on any individual browser--software is complex and it's hard to determine what combinations of web features will wind up being widely used. I do think it's a shame when this happens because sites don't get tested in anything but Chrome. There's no excuse when large companies release webapps and don't test in multiple browsers.

(Disclaimer: I work for Mozilla.)