Most of the graphics over at addons.mozilla.org are blurry when using a DPI > 96 and full page zoom. This is especially true of the screenshots for add-ons which makes some of them unreadable. Personally I use a dpi of 120. Text zoom is not much help as the site seems to have small text to begin with. The layout of the site gets really messed up when text zooming.
To be sure, AOM is not the only site with this problem but as it’s a Mozilla site I would think it would be redone to support high resolution graphics.