For some reason, Firefox (v43.0 / Ubuntu 14.04) isn't properly scaling up the new logo when zoomed in:
The background scales fine, and so do e.g. the vote buttons (which come from the same sprite sheet as the logo). I suspect the problem may have something to do with the filter effect used to create the subtle drop shadow on the logo, but that's just a wild guess.
On Chromium (v47.0.2526.73), the logo does scale up just fine, so this is presumably a bug / quirk of Firefox's SVG rendering. It would still be nice to find a workaround for this, if practical. (Of course, the whole issue is pretty minor anyway, since the logo looks fine at normal size, so I can totally understand if the decision is not to bother fixing this. But I figured it was worth reporting, at least.)