2009 Mac Pro web images problem

Have a question about a lack of sharpness on web images when viewed on my 2009 Mac Pro.
Attached are two screen captures to illustrate what I am talking about. The first is with my 27" cinema display connected to a 2011 MBP. Image shows nice sharpness.

Second is with the display connected to my 2009 Mac Pro. Image is clearly lacking in detail/sharpness. I have tried both the standard nvidia GT120 vid card and a Radeon 7950 in the Mac Pro. Both show the same artifacts.

Any thoughts?

MBP

Are you 100% sure the Mac Pro is set to the native resolution of the display? It looks how things tend to look when the display card is running at a slightly lower resolution than the display.

Yes, proper resolution.

I should maybe also mention that this is a 2009 Mac Pro flashed with 2010 firmware to run dual 3.46 GHz X5690 Xeons.

And this problem occurs in all browsers. But strangely enough, everything is still tack sharp when editing in lightroom or photoshop.

It sounds like the display card on the Mac Pro is running in HiDPI mode. On a retina Mac this is the normal mode and Adobe Photoshop and Lightroom both bypass the scaling layer for their main display viewport, such that the actual photo is displayed at the native retina screen resolution. Browsers and other applications generally have all their graphics sent through the Quartz scaling layer that downsamples them to show at some fraction of the screen's actual resolution, typically half resolution on both axes. Anyone who has a retina iMac or MBP has do doubt noticed that images look WAY better in PS and LR than when you export them and look at them in a browser.

The question is, why is this happening on your cinema display and Mac Pro, when there is no retina screen involved? I do not know the answer to this, and a few minutes Googling it didn't get me very far. It may be something to ask in Apple's own support forums where it will reach a wider base of people who've potentially dealt with this glitch.

So, it seems to be a problem related to my user account.

If I log in under another account. Everything works fine.